Totoro

Well, this is interesting.

Did some reading and it looks like clams keep their zooxanthellic symbionts nutrient limited to force them to pump out sugar, just like coral. The clams' resident population of zooxanthellae doesn't significantly ramp up in response to increased nutrient levels, but on the other hand, clams do respond positively to NH3 and PO4 enrichment -- moreso than feeding them algae, their normal food. Turns out PO4 is necessary for shell growth, which can be limited by either PO4 or Ca levels.

On the downside, nutrient consumption by juvenile giant clams is described as "limited" and worse, there's some evidence that what may be going on here is that clams are improving the coupling between the pelagic and benthic environments -- that is, they're facilitating the movement of nutrients out of the water column and into the substrate. Basically, by absorbing nutrients (which they will continue to do even when their growth is limited by insufficient light) and excreting their feces onto the surface of the substrate, they're concentrating the available nutrients and making it easy for the bacterial community in the substrate to access them. From what I gather, however, oysters and mussels are much bigger offenders in this regard than clams -- in low light, clams will reduce their nutrient uptake, while oysters will go right on sucking in everything they can get and excreting what they don't need as "pseudofeces".

But it was also noted in one paper that "it is known that several specimen being kept in one aquaria are able to deplete nutrient values considerably" -- and that conclusion dates back to 1994, so the aquaculture guys have obviously been hip to this for quite some time. You gotta figure that if they've signed off on it, it's probably a viable technique that we should be thinking about stealing... Though I do worry that the aquaculture crowd isn't oriented towards "permaculture" setups like we are -- their goal is typically short-to-medium term maximization of biomass output, and then they reset the system after each batch gets sent to market. Improving benthic/pelagic coupling (ie, increasing the rate of P accumulation in the substrate) may not be an issue for them.

Anyway, if anybody wants to get all science-y about this, the most relevant and accessible paper I found is here: Physiological performance of giant clams (Tridacna spec.) in a recirculation system by A. Kunzmann, from the Proceedings of the 11th International Coral Reef Symposium, July 2008

So if PO4 is only 5% or less of the total P in the water then our Phosphate test kits are only showing a fraction of the total problem?

Test kits are showing only a fraction of total P in the system, yes, but they're showing the most important fraction. I have a recollection of seeing mention in online forums of test kits that can apparently measure organic P as well as PO4, but IIRC best practice in a laboratory setting is to convert all organic P to PO4 and then measure that -- and in any case, I can't see that measuring total P or organic P would be at all useful to aquarists.

PO4 concentration in the water reflects the overall P level because, broadly speaking, the water column is in chemical equilibrium with the substrate and PO4 is in equilibrium with the other, non-detectable states that P can exist in. In principle, PO4 is even in equilibrium with biologically sequestered P over the medium to long term, as the organisms sequestering P will eventually die and release their stored P during decomposition. Biologically sequestered P can turn over very quickly in the case of small organisms like algae and bacteria -- sometimes in a matter of hours -- or much more slowly, potentially taking years or even decades in the case of fish and other large organisms. Realistically, though, hobbyists diligently remove dead livestock from their tanks, which of course exports the P (and N and S and everything else) they contain.

It's important to note that "equilibrium" doesn't mean that P in the water is equal or close to P in the substrate. Phosphate concentrates in anaerobic areas because it can remain soluble there (the solubility of calcium phosphate, which in its several different forms is collectively the most common PO4 precipitate in SW, is governed by pH, and anaerobic water is generally somewhat acidic -- which would explain why aragonite and white sand DSBs are prone to noticeable shrinkage over time, it crosses my mind). In the overlying water column, PO4 wants to precipitate out -- which, BTW, is why the entire system doesn't crash from skyrocketing P when you mess around with your substrate: hiding in the cloud of fines and detritus that gets stirred up is a cloud of P precipitates. Thus, the natural equilibrium is a whole lot of PO4 in the substrate and a little bit in the water, so by the time PO4 rises to detectable levels in the water, there’s already a substantial accumulation in the substrate.

Also as it gets more concentrated in the sand bed and starts to leach out would you not be able then to remove it from the system throu one of the multiple choices for nutriant export?

Yes. That's how P is managed with chemical scrubbing -- removing P from the water pulls more out of the substrate to maintain equilibrium. This brings down the overall level of P in the system, but hobbyists will stop scrubbing when they reach an equilibrium between the water column and the substrate that puts an acceptably low level of PO4 in the water. And then, of course, P begins to accumulate again...

Which is one of the reasons I don't like chemical P mitigation -- it's a treadmill you can't get off of.

ALso the organic P be able to be able to be removed by our protien skimmers?

To some extent, yes. Bacteria and organic matter removed by skimming carry away the P sequestered therein, but obviously this isn't enough to mitigate the problem or skimmed systems wouldn't show P accumulation.

Don't stress too much over it. When talking about nutrient cycling in broad terms, there's often not much need to differentiate between different forms of the nutrients involved because they routinely switch back and forth between them. Even scientists write about N and P, so you get sentences like this:

"A classic example of the mechanisms of inertia is formed by the P release from sediments; in pristine systems, sediments act as a sink for P, but on increasing eutrophication the ability of sediments to capture P often decreases." (from N:P Ratios in Estimating Nutrient Limitation in Aquatic Systems by Petri Ekholm, 2008)

But here's the little science lecture, if you're interested...

P is the symbol for the chemical element phosphorous.

Orthophosphate = phosphate = PO4 = one atom of phosphorous and four atoms of oxygen

PO4 is actually an ion; the complete molecule is phosphoric acid: H3PO4

H3PO4 breaks up in water to 3 H+ ions and the negatively charged PO4 ion.

PO4 is highly reactive and wants to precipitate out of oxygenated seawater (edit for FW aquarists: and also hard FW) at the drop of a hat. PO4 is sometimes called inorganic or mineralized phosphorous. It's the only form of P useful to plants, including algae, so the fact that there's not much around makes it the most common limiting nutrient for autotrophs.

Considerably less than 5% of total P in natural waters is PO4; in surface waters where photosynthesis takes place, PO4 is likely less than 1% of total P. The rest is organic P -- ie, P that has been consumed and incorporated into biological molecules like amino acids and proteins.

Most organic P in the water column is biologically sequestered inside plankton and fish and other organisms. I don't have numbers for the marine ecosystem, but in FW lakes, 70% of organic P is biologically sequestered in the trophogenic zone (...the upper levels of a lake where primary production and life in general happens). In surface waters where photosynthesis takes place, over 95% of total P may be biologically sequestered. The remaining organic P is either dissolved or in colloids, a sort of intermediate phase between being dissolved and being particulate matter. An individual atom of P may change between these four forms -- free range orthophosphate, colloidal phosphorous, dissolved organic phosphorous, and biologically sequestered organic phosphorous -- either through biological activity (like being consumed by algae or excreted by bacteria) or physiochemical processes (which can shift P between dissolved organic P, colloidal P, and orthophosphate).

Does that make it better or worse?

Really basic question for you. If cyano would infact grow at a pace where it could be used succsessfully to remove P from a tank' date=' then why is it people have such a hard time getting rid of it? Some people fight it for many months. Some tanks have patches for years.[/quote']

 

The trouble with basic questions is that they appear simple on the surface, but they encompass so many variables and imponderables that a simple answer is difficult...

 

But perhaps the simplest answer is already there in your own words: people fight cyano. It seems unreasonable to complain that there's no anecdotal evidence of cyano being used to effectively export nutrients when the usual response of hobbyists is to do whatever they can to prevent its growth.

 

You're obviously a much more experienced hobbyist than I am -- are you aware of anyone going in the other direction and trying to cultivate cyano so they could physically remove it from the system to export nutrients? I'm not talking about a scrubber, but something simple and obvious like letting it grow in the sump or not pointing a powerhead at a cyano bloom in the DT and trying to make it go away with high flow. Though it may well be impossible to grow enough to make a difference in a reef tank, given the overall high flow conditions... Small organisms like to exploit the boundary layer, which reefers are consciously trying to disrupt.

 

 

If it were effective at nutrient removal' date=' wouldn't the course of action for cyano be to let it run it's course as it would end very quickly when it consumed the available phosphate?[/quote']

 

I'm in uncharted waters. I don't have any good information on how quickly cyano can pull P out of the substrate.

 

My intuition is that something that takes long time to happen will take a long time to undo.

 

 

IME your ratios are a bit off. I guess it would depend heavily on the type and amount of food used. The main food I feed my tank is very low in phosphates with the manufacturer claiming that the max ratio is .o1%.

 

Ah, fair point -- my bias is towards homemade foods. Didn't stop to consider low-P commercial products.

 

But if P accumulation is a problem even with low-P food, then it would seem intuitively obvious that whatever algae is being used to export nutrients must be really, really bad at exporting P...

 

 

Your first and second choice involve using bacteria, your third choice involves removing the bacteria you advocate in your second choice. Kind of odd. ...

 

Lil backwards mate. Shimek claimed far superior results with the bigger footprint. He continues to report the size is needed for bacteria and microfauna production for the bed to be effective longterm. People using the smaller buckets get good results for filtration, but the food production, and creation of a living bed is not achieved. ... I think part of the way DSB's can sustain longterm is the fauna that grows in them as well. It's not all chemistry, there is some biology in there as well.

 

And don't I feel foolish for cobbling together a purely physiochemical model and forgetting that the chief selling point of DSBs is that they provide habitat and food. Been a while since I read up on this stuff, and obviously my bias is showing -- as I said in the other thread, I'm an oceanographer by temperament, not a marine biologist. You're absolutely right: I made the mistake of looking at this entirely through the lens of chemistry. So, let's reconsider in the light of biology...

 

Biologicial sequestration of P dominates in oxygenated DSBs -- that is, the phosphorous is locked up inside living organisms. In anaerobic DSBs, or any anaerobic substrate including the interior of live rock, chemical sequestration of P is the dominant mode.

 

Biological sequestration -- which is the natural bias of a good marine biologist, I totally get that -- may actually interfere with chemical sequestration in a DSB and, overall, hurt more than it helps because benthic fauna stir up the sandbed and keep it oxygenated to a much greater depth than would be the case in their absence. Two pictures are worth a thousand words: http://www.baybenthos.versar.com/benthos.htm

 

Chemical sequestration can store away MUCH more P than biological sequestration in a substrate with a high surface area-to-volume ratio, such as benthic mud or a DSB or even the tiny pores and fractures within LR. This is because PO4, which can persist in anaerobic conditions and will not precipitate out, likes to adhere directly to the surface of minerals.

 

Like everyone else, I feel I have more than enough chemistry to keep track of in oxygenated water, so here's my E-Z conceptual shorthand for anaerobic chemistry: it's Bizarro World. Chemical reactions that we take for granted, like free PO4 and Fe wanting to precipitate out as soon as they hit the water, all run in reverse. In fact, the insoluble precipitates that can be so irksome to us are food for the bacteria in Bizarro World. Orthophosphate, so rare and precious in oxygenated water, is a primary waste product of methanogenic bacteria -- those are the ones at the bottom of the "layer cake" of anaerobic respiration pathways in marine and freshwater sediments:

 

                                        SEAFLOOR
*******************************************************************************************
---- (oxygenated sediment - aerobic respiration) ------------------------------------------
---------------- (nitrate reduction) ---------------- where odorless N2 gas is made -------
--------------- (manganese reduction) -----------------------------------------------------
------------------ (iron reduction) -------------------------------------------------------
----------------- (sulfate reduction) --------------- where super stinky H2S is made ------
---------------- (methane [b]pro[/b]duction) --------------- where odorless CH4 is made ----------

After that, it's methanogenesis all the way down. And also Mn and Fe reducers, but nitrate and sulfate
reducers are restricted to their zones. Note that all zones overlap to some extent, so the upper sulfate
reduction zone overlaps with the lower iron reduction zone, for example, and the lower sulfate reduction
zone overlaps with the methane production layer.

And here's a fun fact to break up the lecture: H2S + CH4 = "swamp gas" -- stinky and flammable!

 

If they're not Fe-limited, the iron reducers will outcompete the sulfur bacteria and methane makers below them for carbon, which is what they're all after. In the real world, between that and the general scarcity of food (organic carbon) on the floor of the open ocean, bacteria in the bottom two layers don't generally see much action unless, like, a whale carcass lands on top of them or something. Closer to shore, bioturbation (critters turning over the mud or sand) tends to stir up the top three layers and allow organic carbon to percolate down to the lower layers. This brings food to the sulfate reducers... Y'know that foul, stinky black gunk in the substrate? Yeah, that smell is H2S from the sulfate reducers -- and if you got sulfate reducers, you got methane producers, which is significant because they're the end of the line...

 

Here's the basic biochemistry of methanogenesis from one of my books:

 

[x CH2O] + [y NH3] + [z H3PO4] = [x CH4] + [x CO2] + [2y NH3] + [2z H3PO4]

 

This is of interest to any fishkeeper because it runs in surplus where NH3 and H3PO4 are concerned -- twice as much comes out as goes in. The extra N and P don't appear by magic; they're in the food the bacteria are eating. See, the bacteria are really mostly interested in organic carbon, which is often the limiting nutrient for them (...and that's why vodka dosing works, incidentally, which I mention not to show off but to demonstrate that this line of thinking is consistent with The Hobby As We Know It -- turns out Bizarro World isn't that bizarre in some ways), and all the stuff that's attached to the carbon is kind of in their way.

 

Crucially, the chemistry of methanogenesis shows that in Bizarro World, biological sequestration doesn't work -- it cannot work. The limiting nutrient for the anaerobic bacterial community in the substrate is carbon, so nitrogen and phosphorous are in surplus. N and P don't end up locked away inside anaerobic bacteria, they're unwanted waste products, like oxygen is unwanted waste for plants. The N is soluble in oxygenated water and can diffuse out of the substrate to be captured by autotrophs, but the P is stuck.

 

The flipside of this is that chemical sequestration doesn't work in oxygenated sediments. So in oxygenated DSBs, P storage is essentially a function of overall biomass.

 

In anaerobic conditions, not only is P stored efficiently in the substrate, but the bacteria are actively putting it there. This is the basic mechanism of P accumulation -- it's driven by C-limited anaerobic bacteria, but the reason P actually accumulates is chemical sequestration. It's P sticking to the mineral surfaces atom by atom. Well, really it's PO4... but then, there's just the one atom of P in each ion, so... okay, I'm sticking with "atom by atom", and the purists can just call it poetic license.

 

Anyway, that's why I think a remote deep mud bucket would work -- simple chemical equilibrium should eventually diffuse enough P into the anaerobic mud to export a useful amount. Bacteria can only speed up the process.

 

So... When you say "buckets get good results for filtration", pledosophy, that's unclear to me, and as you might imagine, I'm curious... Exactly what do you mean by "good results for filtration"? Is that NH3 --> NO2 --> NO3 type filtration, or general nutrient (including P) removal?

 

 

I am not referencing the Standard Model or Santa Monica's theories.

 

Yeah, I know. This is all kind of OT. I'm not impressed by SantaMonica's thinking, myself, and I'd really rather be defending the Standard Model than trying to untangle a pile of anecdotal information about deep sand beds on the fly, but then again, there doesn't seem to be much discussion of anaerobic environments in the hobby, so maybe this will be helpful.

 

The way I like to look at it, last year my big epiphany was about bacterioplankton, so I was about 35 or 40 years behind the real oceanographers. This year, it's P ratios, which puts me about 25 or 30 years behind -- so I'm totally catching up!

 

 

As for the old tank syndrome' date=' I am really not all that worried. I have seen no evidence that is a real thing[/quote']

 

And you wouldn't, if you chemically scrub your system to control P.

 

But if you're truly able to maintain a reef tank over the long haul using nothing more than green algae to export P, you're my hero. Even if you're using low-P commercial food, I'm impressed. Do you have any write-ups of your tank management practices online? This deserves close study, as I'm all too aware that what I'm doing isn't a viable approach to the P problem.

Seriously? You think I'm that well organized, MVP?

My cunning plan is to remove one piece of LR and change out the half of the sandbed underneath it. Hopefully, while the LR is soaking in FW for what I'm guessing will be a few months to leach out the accumulated P, the new half of the sandbed will be colonized. Then the dead LR goes back into the tank to be brought back to life. When I'm happy with that process, the other piece comes out and the other half of the sandbed gets replaced.

This won't get me back to zero, as both the new half of the sandbed and P-free LR will absorb P once they go into the tank... So, best case scenario, I remove half the accumulated P by removing half the substrate, then P equalizes and I remove half of half and get down to 1/4 of whatever level it is that finally prompts me to action. Though, of course, it's a dynamic system, and P will still be accumulating during this process... I figure worst case, I'll end up getting about half of the accumulated P out of the system this way. I'm thinking that would be enough to buy me another couple-three years, maybe more.

So my sand bed gets full of phosphate' date=' and I use algae to export that nutrient. Why would the algae just not absorb the added phosphate from the sand bed when and if it started leaching? ... Why would the natural process not work with stored P.[/quote']

 

It totally does. A substrate leaching P is generally a recipe for a cyano bloom: http://www.pnwmas.org/forums/showthread.php?31036-Cyano-bactiria&p=300357&viewfull=1#post300357

 

Let it bloom, remove it; repeat until it pulls enough P out of the substrate to lose its competitive advantage and stops blooming. That looks like a viable avenue for nutrient export. In fact, that's the first thing I suggested be tried to determine if a cyano scrubber could work: pick a spot where cyano wants to grow, anyway, and start helping it instead of fighting it. Let's see if we can actually grow enough of the stuff to make a difference.

 

The idea of a cyano scrubber is nothing more than to set up a special corner of the system just for cyano, where it'll be so happy that it grows there all the time... Think of an algae scrubber as a permanent, artificially maintained algae bloom.

 

 

In reference to removing the live rock every few years' date=' it kind of goes against the whole constructive ecosystem standpoint.[/quote']

 

I agree. That's why I'd like to find a way to avoid it.

 

Bioremediation (a cyano scrubber) is my first choice. Failing that, I'll try going with simple chemical equilibrium (a remote deep mud bucket). Plan C is soaking my LR.

 

Well, actually, Plan C is probably shutting down and trying something new. I really only set up the marine tank for curiosity's sake, and it's pretty well served its purpose at this point, I must say...

 

 

Phosphate+Nitrate= algae for the most part. ... If your rock is absorbing phosphate and your goal is to control the tank using biology at that point would you not just increase your algae population' date=' or change your pruining style to increase growth[/quote']

 

No disrespect intended, but the Standard Model says algae is not about addition. It's about ratios. I'm obviously not the first hobbyist to catch on to this: http://www.barrreport.com/showthread.php/4018-Comparing-N-P-ratios-and-critical-cocnetrations-in-aquatic-plants-algae?

 

The N:P ratio is the heart of the problem. Broadly speaking, the cells of phytoplankton are the richest among the primary producers in nitrogen and phosphorous, followed by the "higher plants" (marine and FW angiosperms) which are substantially poorer in P and somewhat poorer in N content than phyto, and macroalgaes have the lowest N and P content of all aquatic plants, with an average C:N:P of 550:30:1 and an average protein content of less than 1/3 of phyto's average of 50% protein. Note, however, that the phytoplankton divide between true algaes, with N:P ratios of 20:1 or more, and the cyanobacteria, with N:P ratios of 10:1 or less (...though it wouldn't surprise me if a few organisms prove to be exceptions to this tidy division, like for example a P-rich algae -- BBA seems an obvious candidate).

 

The upshot is that the N:P ratio of green algae (especially tropical macroalgae, FYI, which have an average N:P ratio of over 40:1) is higher than the food going into an aquarium (which I'm assuming is 16:1 -- the Redfield ratio -- but may well be enriched in P, what with amino acid supplements and whatever else people are feeding their corals and blending into their fish foods). This means that green algae cannot mitigate P accumulation without supplemental N, and therefore over the long haul, green algae cannot prevent a tank crash due to P saturation. Doesn't matter how much algae you have or how fast it grows. If the N:P ratio of what you're using to export nutrients is higher than the N:P ratio of what's going into the tank to feed the livestock, you're going to be left with surplus P. However it's executed, I believe the concept is, as the title of this thread suggests, fatally flawed -- it's possible run a balanced system with regards to N using green algae, but not P.

 

Cyanobacteria can fix N, so it'll grow in N-limited environments like a system based on green algae where N is well controlled, and cyano has an N:P ratio lower than the food going into the aquarium, making it a viable choice for P mitigation. So, yes, the goal is very much to increase the algae population, but we need the right algae...

 

 

Your question if a remote DSB was ever constructed' date=' several have been. ... There were some people who adapted these style of sandbeds into modular units by tying multiples together. I tried this myself but never found much benefit likely IMO because of the already large population of algae that I use in my systems.[/quote']

 

Ah, thank you -- I know remote DSBs were The Next Big Thing a while back, but I was never sure if anyone actually tried modular RDSBs. Interesting that it was modular Rubbermaid trash cans, though, as when I mentioned a modular RDSB, I was thinking more along the lines of the modules being some five-gallon buckets submerged in a plastic horse trough or an old 75 gallon glass tank, for reasons that will become clear (I hope!)...

 

 

I believe it was Shimeks writing about the lack of overall value they would have if the footprint was less then 4 foot by 2 foot and the depth was less then 18"' date=' however many people using a 5g bucket on a 100g or so system reported great results. Best reported results came if the bucket was covered and no light was allowed in.[/quote']

 

This looks a bit like a straw man to me, but what the heck... Nobody's taking a run at the Standard Model, so let's kill some time thinking this through.

 

First off, let me make clear that I'm not advocating some particular method of tank management involving deep sand beds... Derbird asked a specific question, and I gave him a specific answer. I do not maintain it is the only viable answer, and I just mentioned DSBs conversationally in reference to the "remote deep mud bed" I described in the thread over at algaescrubber.net: http://algaescrubber.net/forums/showthread.php?2208-cyano-scrubber-and-also-mud&

 

DSBs are (or were) made with relatively coarse sand in order to facilitate the movement of water and nutrients into the DSB. IIRC, pool filter sand was the medium of choice, and from what I remember reading about the guys who were trying to turn old 55G tanks into RDSBs, they all plumbed them to flow end-to-end, thinking they'd maximize contact time with the sandbed as the water passed through. But I think the pool filter sand and the dynamics of water combined in an unforeseen way...

 

Seems to me the reason the plastic bucket brigade reported better results than Shimeks (or whoever it was) is that large rectangular footprints work against establishing an effective nutrient sink by providing a lot of surface area for the oxygenated water flowing over the top of the sand bed to interact with the water within the DSB. To my way of thinking, the strong, more or less unidirectional flow in a rectangular RDSB is essentially a river tank... I've read up on rivers as well as lakes, and when flowing over a coarse bed of gravel or sand, river water flows in and out of the upper substrate in much higher volumes than I would ever have suspected from casual observation. The intuitive assumption that the sand offers so much resistance that any flow within the sandbed will be negligible when the water has a free and unobstructed path on top of the DSB turns out to have no support in the scientific literature -- quite the opposite, in fact. Subsurface currents are much slower than running water, but part of the "river" flowing through a large footprint, rectangular RDSB would flow unseen through the top of the sandbed. Indeed, as I understand it, that was largely the point of using pool filter sand... and I think it worked entirely too well.

 

Hydrodynamic forces -- meaning the current in the upper layer of sand dragging DSB water along with it sort of like the way suction from the water flow from a faucet gets the siphon started for a water change -- slowly but steadily pulled water through those old, large-footprint DSBs and flushed them out, preventing significant accumulation of nutrients in the interstitial water of the DSB's anaerobic zone. Once a new DSB came into chemical equilibrium with the system it was plumbed into, its capacity for nutrient retention largely consisted of the resident population of bacteria and benthic organisms; P and other nutrients that normally build up in the anaerobic zone were instead flushed back into the water column by water circulating through the anaerobic zone. Even N2 gas generated by NO3 reduction in the uppermost anaerobic layer of a DSB readily dissolves back into the water -- I was able to all but eliminate offgassing from a 5" sandbed in a 10G FW hex by inducing a very, very small circulation through it with nothing more than an uplift tube from an old UGF jammed down into the sand in one corner of the tank (...I call it a "ventilated deep sand bed"), so it doesn't take much subsurface flow at all to pull stuff out of a DSB. But if you do that, it's not good for much beyond converting NH3 to NO3. So as a result of circulation within the sandbed, a new large-footprint DSB would only potentially consume detectable amounts of nutrients as it came into equilibrium with the system and cycled, and then it wouldn't do much after that.

 

The problem was the intuitive bias that permitting flow within the DSB itself was necessary to ensure adequate nutrient exchange between the water column and the DSB. The bucket brigade accidentally solved the problem by building DSBs that were tall, narrow, and round, and as a result had poor internal flow even though they were using the same sand. Because of the smaller surface area and less organized surface flow in a bucket DSB, the hydrodynamic pump effect wasn't strong enough to turn over the water in the anaerobic zone. Instead, the plastic bucket DSBs relied on diffusion, not flow, to get nutrients to their lower layers, and the water there turned over very slowly, allowing P accumulation to take its natural course.

 

This theory is consistent with the observation that a large-footprint rectangular remote DSB had to be extra deep to function effectively as a nutrient sink -- to compensate for the coarse medium permitting easy water movement within the sandbed, it had to be deep enough that the bottom of the DSB would be outside the circulation pattern and nutrients could accumulate there in peace. Not sure what to make of the Rubbermaid trash cans, though... I take you at your word that multiple RDSBs had no effect, but if other people are still running theirs, apparently they think they're working. There may be ways to set up the hydrodynamics in round containers to generate slow circulation way down deep in the sandbed and flush them out, or maybe the ones that work are in tall and narrow containers, and the ones that don't are in short, squat containers. Can't work it out farther than that without more data, I think.

 

But, as I pointed out in the other thread, I think a remote deep mud bucket would be an effective P sink. Wouldn't fix the problem, but it would put off the day of reckoning.

 

 

there really is not just one way of keeping a successful reef tank everyone has there own ideas and ways of making it their own tank and thats the point isnt it to have your own part of the ocean in your house

 

Could not agree with that position more strongly, Blackhand.

 

If you have a successful tank, keep doing whatever it is that you're doing -- my job is not to convince you to follow me over the horizon, but simply to report in when I think I've found something interesting.

Iron. Right. As micronutrients go, that's a big one.

I do have a couple of pieces of good information on how iron affects the structure of algae communties. First, cyano needs Fe in a big way because the enzymes involved in fixing nitrogen are known to be very iron-rich, and growth using N2 as a nitrogen source can require as much as 10x more Fe than autotrophic growth using NH3 to supply N. Autotrophic growth on nitrate also requires iron-rich enzymes to convert NO3 to NH3, BTW, but less so than cyano.

Iron is the only micronutrient known to be limiting for marine phyto in the wild -- one estimate suggested that phyto is Fe-limited in as much as 40% of the ocean's surface waters. Iron is so important that when it's the limiting nutrient, bacteria (including cyano) and some algae secrete what are essentially tiny chemical nets, called siderophores, around themselves to sweep up iron from the water atom by atom. Neat, eh?

Organisms without siderophores are adapted to capture iron that's complexed with organic molecules. Broadly speaking, then, iron complex supplements should favor green algae. Electrokate, I would speculate that the algal symbionts inside corals can't form siderophores -- what good would they do in there? -- which could explain why corals might benefit from iron complex supplements. A chelated iron supplement, however, would probably not provide any benefit, as the whole problem with obtaining iron in the wild is that in NSW, what little Fe is available to begin with mostly gets locked up by chelation. In the absence of any other information, this might explain anecdotal, hit-and-miss success with iron dosing.

How do you avoid the "old tank syndrom"? Which if I read right is a build up of PO4 in the sand bed. Do I need to change out my sand bed from time to time or is there a better way.

Yes, you change out the sand bed -- not all at once, though -- and soak the LR one piece at a time when rising P becomes an issue. Should take several years in a well-run tank, though, so don't panic. And probably most tanks don't stay up that long, anyway, so it's a non-issue for the majority of hobbyists.

I've read online about people considering modular remote DSBs so part of the sandbed can be changed out every year. Don't know if anyone's actually built such a thing, but I acknowledge that this type of thinking is where I got the idea for a "remote deep mud bed" to pull P out of an existing substrate.

Much the same question was asked in the other thread, Jeramy, and this is my response:

The name of the game is bioremediation. If you're satisfied controlling P through chemical means, I'm not going to tell you you're wrong, but please understand that from my perspective, that method is philosophically unsatisfactory. It's also energy-intensive (I'm speaking more of the manufacturing process than the implementation) which expands the carbon footprint of a hobby that's already pretty resource-intensive, and from a more practical standpoint, it can get pricey over the long haul.

Plus, as Floyd pointed out in the other thread, even the manufacturers acknowledge in the fine print that chemical scrubbing is more about controlling P in the water column than mitigating P accumulation in the substrate.

Whoever it is that's been going into every thread I post in and rating it five stars -- well, first off, thanks for that, but also, you may find this interesting:

http://algaescrubber.net/forums/showthread.php?2208-cyano-scrubber-and-also-mud&

I also feel I should say a couple of things to the Pacific NW Marine Aquarium Society...

First, thank you for tolerating my lectures while I've been thinking this through. No, I don't have a book deal or a product to promote or anything of that sort -- I'm a hobbyist, just like you, except I'm more interested in the stuff you can't see in a fish tank than the stuff you can.

And secondly, I apologize for not pointing out earlier that algae scrubbers can't keep up with P input in fish food, and thus scrubbers cannot prevent "Old Tank Syndrome" and a system crash due to P accumulation in the substrate. I caught on to the problem a while ago but thought it would be unkind to harangue poor Kia over this, so I waited until a possible solution dawned on me and then, in what was meant to be a gesture of respect, made my case directly to SantaMonica in his algae scrubber forum.

SantaMonica appears to have opted out of the discussion, which suggests to me that either he is unable to refute my position or he was already aware of the problem and just hoping against hope that nobody else would catch on, so I now feel it is appropriate to bring this to the attention of others.

And as the title of this thread suggests, I also posted what I tentatively call the Standard Model of Aquarium Algae in that thread, and the Standard Model should be of broad interest to hobbyists -- if, of course, I've got it right -- so I encourage anyone who finds my ramblings interesting or enlightening to take a look.

Finally, if anyone out there can drive a truck through the Standard Model, please do so loudly and publicly. I enjoy staring at my fish tanks and trying to figure out what's going on in there, and coming up with the Standard Model was like reaching the last page of a good book...

As it was explained to me, the plastic barrel color coding works thusly:

BLACK = contents are hazardous or toxic

BLUE = contents are on the GRAS ("Generally Recognized As Safe") list and not considered hazardous or toxic -- note that some food-grade flavorings and ingredients, such as citric acid, are shipped in blue barrels, but on the other hand, so are all manner of industrial chemcials like DMSO...

WHITE = contents are actual food or the basic ingredients of food (like vinegar, soy sauce, etc.)

So look for white barrels, and you won't have to stress over stuff like this.

This may be helpful:

http://www.gpas.org/e107_plugins/forum/forum_viewtopic.php?10366

One-piece, injection-molded plastic fish tank trim is STRUCTURAL.

Most glass aquaria sold today are substantially understrength because one-piece plastic trim holds them together and allows the manufacturers to get away with using thinner, lighter, cheaper glass. Even in small tanks, the silicone adhesive is marginal without the trim backing it up. One-piece structural trim basically acts like two straps that hold a tank together at the top and bottom.

On the plus side, structural plastic trim is the reason we have Petco's dollar-a-gallon sales and why we take glass monster tanks more or less for granted nowadays, but the downside is that these tanks are all rather fragile... Seemingly cosmetic damage to structural trim (...and if anybody has a better turn of phrase than that, I'm all for it -- "structural trim" sounds like a sexual euphemism from Flatland), such as a cracked corner, can fatally weaken an aquarium, and removing the trim for aesthetic reasons is just asking for trouble.

If you want a rimless glass aquarium, fine and dandy, but this is not a good way to go about it. Better to build one yourself or buy one at the LFS.

I'm pretty proud de rimmed it myself!

Having broken a few tanks, myself, trying to get that #%@$*&! plastic trim off, I salute you.

...dark yellowish green water...

 

...my scallop, and snails go crazy as the water gets darker, the scallop starts to feed like mad on things in the water...

 

...I have little spots on top of the water now, thousands of little whitish/clearish specks that almost look like they could be offspring...

 

...looks like all the hatchlings got eaten, they almost resembled little shrimp...

From how you describe the color and the delighted livestock, this sounds like a diatom bloom: first, the algae blooms, then you get a zooplankton bloom that clears your water, and then the pod population crashes when they run out of diatoms to eat. As their teeny-tiny corpses decay, they release the nutrients they consumed back into the system and set the stage for another algae bloom.

And this looks to me like a possible smoking gun:

I have to use tapwater for my water changes

Check with your water utility to see if you have dissolved silicates in your tap water. Diatoms will outcompete green algae for phosphorous at high Si:P ratios.

Also, this fits:

this started happening shortly after this tank finished cycling

Newly established tanks typically have very low phosphorous levels, so if your tap water has any measurable silica content, the diatoms are in business.

It's worth noting that newly set up aquariums often display the same progression of dominant algae types typical of the annual population cycles seen in freshwater temperate lakes and ponds: first you get a diatom bloom, then a green algae bloom (this is normally a phyto bloom in the wild, but we usually just get green nuisance algae), and then a cyano bloom. This progression also happens in tropical lakes (...and fish tanks!) except the clock is never reset after cyano takes over because there's no winter.

As for what to do about it, Islandoftiki is exactly correct: treat the problem, not the symptom. Most anything that eats algae loves diatoms, which means that right now, the symptom is resolving itself -- over and over and over again. But the delicious and nutritious diatoms are getting preferentially consumed while nuisance algae is ignored. Over time, this will select for nuisance algae in your tank, and as phosphorous gradually accumulates in the substrate, the competitive advantage the diatoms are now enjoying over the green algaes will go away. So unless you can either export your way out of your predicament or identify and address the source of the excess nutrients, at some point your diatom blooms will stop and your real algae woes will begin.

Ye gods! 500 gallons is well over TWO TONS of water -- and your client wants small and quiet?!?

I'd suggest you consider bagging the idea of solving this through the usual channels and instead step up to a small industrial chiller. A unit with a remote pump/condenser would solve the noise and size issues, but it would also require a fixed installation (...perhaps not such a big deal with a 10x4x3 tank!) and lots of extra piping, which increases the chances of a leak developing. Everything's a trade-off.

To find a reliable local vendor, try talking to some folks in industries that routinely use such equipment: breweries, fish hatcheries, dairies... If you have any contacts or clients at Intel, they may be able to point you in the right direction, as well, as I understand the semiconductor industry needs lots of cool, clean water for their fabs.

Is the glass 3/8" or 1/4"?

If it's 3/8" thick, you may be better off reassembling the aquarium in its original configuration, as those Old School tanks are substantially tougher than what's on the market nowadays. Modern tanks in the 40-55G range that are made with 1/4" glass rely on the plastic trim for a significant portion of their structural strength. And in any case, the thicker the glass is, the dicier it is to cut it cleanly...

If it's 1/4" thick, you may find reading this to be worth your time: http://www.austinglass.com.au/The%20secret.htm

I've cut 1/4" glass before, and it's pretty straightforward -- but sanding down the rough edges so you don't open up an artery is tedious work and absolutely not to be neglected.

I can also take the tops off of wine bottles, which turns out to be a useful skill in the fishkeeping hobby... Who knew?

EDIT: Whoops... Spent too long typing! Glad to hear your problem found a solution.

The trick to epoxying fish tank trim is to "flash" the plastic first. Epoxy (even the stuff from TAP Plastics rated for HDPE) won't hold because the polymer molecules nest tightly with one another and present a slick, flat surface. You have to pump energy into the plastic to get the molecules to loosen up a little bit and stick their free ends into the air, thus providing a bondable surface. The industrial process for this is to flash the plastic with very high voltage electricity (that's how they print the art and text onto kitty litter buckets, for example) but us civilians have to use fire. A plumber's torch will do nicely, or you can even use a cigarette lighter if you've got the patience... You don't have to heat the plastic to the point where it's beginning to melt or craze; just be sure to flash the entire surface area you plan to glue. This will buy you 30-60 minutes of working time, after which the plastic will "heal" itself, and paint or epoxy will no longer adhere properly.

Personally, though, I'm a big fan of Old School glass braces, and I agree wholeheartedly with Arsonmfg's suggestion to use 1/4" thick glass over 1/8" window glass from the hardware store -- though I'd go with a much wider brace than two inches. The key metric here is the surface area of the joints between the brace and the front and back walls of the tank, as silicone (and I'm talking about The Good Stuff... milspec RTV 108, not GE sealant from Home Depot) has an adhesion strength of only about 40 PSI, while the silicone itself is much stronger. A proper glass shop should have 1/4" stock on hand, and there's even an outfit in Vancouver where you can get 1/4" tempered glass made to order (...that would be Peninsula Glass, for those of you playing along at home).

But since you're planning to sell your tank, the easiest out here, as has already been suggested, is not to fix it at all and let the next guy worry about it...

Try Peninsula Glass in Vancouver, WA.

http://www.peninsulaglass.com/

You can buy RTV 108 at amazon.com and drillspot.com -- the latter is Grainger's online "front company" which they set up to sell to the general public without diluting their brand.

Drillspot.com also sells RTV 103 black silicone and, for the fashion-forward fishkeeper, RTV 102 white silicone and RTV 106 red. Clear, black, and white silicone cost less than $10 per tube; the red is very expensive at $42.49 per tube because it's made for high-temperature environments (safe to 500F instead of 400F). The entire RTV line is milspec, incidentally.

Drillspot's adhesives and sealants menu page: http://www.drillspot.com/adhesives-sealants-and-tape/?brandid=784

Note that these products are listed as "GE Silicone" even though they're now made by a company called Momentive Performance Products.