Is dKH drop linear?

[Willapa]

I've been using 2 part for the last few years and only briefly got into a good groove when I switched to bicarbonate. I'm trying to dial in my new tank and decided to try ESV Bionic. During my daily testing. I was curious if Alk consumption occurs at equal rates throughout the range. I realize that coral may build their skeletons at different rates during the day than at night, but do they consume more depending on the availability in the water? For example, will they consume more at 9 than at 8? Supplement calculators are truly linear in their calculations, but curious if it is really a curve. I would assume low Alk (below 7) would cause corals to slow down calcium carbonate building. Any thoughts?

[KenH]

In theory, higher alkalinity levels increase the rate of calcification in corals but I think the effect would be fairly modest from the standpoint of calculating dosing rates. So as you stated, within the alkalinity range that is considered healthy for corals it is probably a slight curve but flat enough to assume it is linear.

[MVPaquatics]

The ratio of carbonate vs bicarbonate changes with pH. Not only do corals build skeletons at different rates during day and night, but in a closed system of an aquarium, the ratio or carbonate vs bicarbonate changes during the day vs night due to pH  changes that occur. 

Also, as corals grow, they use exponentially more and more nutrients to continue building. 

I think there are way to many variables to be truly linear. 

Google calcium bicarbonate vs carbonate pH and you can see the relationship.

When I studied corals in college (it has been a few years) it wasn't really know whether corals preferred bicarb or carbonate. It wasn't clearly understood whether they took carbonate up directly or took up bicarb and used a proton pump to spit out protons to make carbonate themselves. 

All in all stability is key. The three are all interrelated. Fluctuation in one level effects all three. Smaller changes are better than big changes. People often shoot for a goal of maintaining say 9 or 10DKH but don't monitor pH, which is critical. 

[The ReefBox]

I think another thing to mention when running the higher end of kh if u are lacking nutrients you will tdnd to see tip burn and pale colors as they are muchmore sensitive to light then say at lower kh levels with a lack of nutrients available

[milesmiles902]

Is dKH drop linear?

Answer: As with any population growth is almost always exponential and their resource consumption grows at a similar rate. Even more so with corals because their population grows with surface area, which is also an exponential process.

[milesmiles902]

Wait, side note: This got me thinking, I wonder if the growth of coral polyps compensates for the growth of surface area. Essentially, they would be linear to each other, but individually exponential...

Either way, consumption is exponential.

[Willapa]

8 hours ago, KenH said:

In theory, higher alkalinity levels increase the rate of calcification in corals but I think the effect would be fairly modest from the standpoint of calculating dosing rates. So as you stated, within the alkalinity range that is considered healthy for corals it is probably a slight curve but flat enough to assume it is linear.

Good point. With that said, you may not see much difference until you reach the real extreme ends of the spectrum that most reefers wouldn't be hitting anyway. So in that sweet spot, the difference sounds like it would be negligible. Plus test kit error comes into play. I switched to a Hanna, but still lots of room for error.

[KenH]

Certainly as a coral garden grows, the demands it places on alkalinity and pretty much everything else grows in a more or less exponential fashion, but the question at hand I believe is looking at the more immediate consumption rate based on the alkalinity level that the tank is run at.

Scenario A - A tank is run at 8 dKH and you have to add X amount of alkalinity supplement to maintain that level for 24 hours

Scenario B - The same tank is instead run at 10 dKH and you have to add Y amount of the same alkalinity supplement to maintain that level for 24 hours.

Does X = Y or is X < Y because the demand is higher with the higher alkalinity level because of increased calcification or other biological processes?

IMO there is probably a slight difference, but it is within the source of error created by the dosing and measurement methods.

[Willapa]

Nicely said Ken, that was exactly what I was getting at. I've just struggled to maintain high alkalinity and just settled for the 7-8 range. Corals seemed to be happy and growing, so just rolled with it. But I always wonder how folks keep it above 9 and thought I might have to crank up my dosing since the consumption rate was going up at higher alk levels. I keep my Mg in check and calcium balanced with the alk, but even so, levels always settle back and maintain in the 7-8 range. I once tried upping the dosing and plastered all of my equipment and rear overflow compartment of an AIO with precipitation. It was like chipping ice off your car! Don't want to repeat that!

I'm getting close to hitting equilibrium with ESV Bionic in my new setup and may try to push it a bit, but will closely keep an eye on precipitation. My last tank was small and heavily stocked and the high pH of carbonate I think was pushing the precipitation. When I switched to good ole Arm and Hammer bicarbonate, the problem went away. The new tank has more stable pH and I'm dosing in small increments directly over the return nozzle, so this should do the trick. But I'm up to 60 ml/day, which seems high for a 50 gallon frag tank that is reasonably full. But if it's not precipitating out, must be getting sucked up by tank inhabitants!

[Gil&Fin]

One thing to think about is making adjustments by using a different brand salt. Every brand has a little different balance, so depending on the needs of your tank, a different brand of salt might work better. For example, I have a heavily stocked system. I was using Kent for years, but battled with very high calcium. If I work to raise alkalinity, I had precipitation just like you Willapa. I've since switch to Fritz and although I initially had some problems, I'm happy with it now. It seems to help keep my levels where I think they should be, and where I think my corals are happiest.

 

Here is a link to a chart that lays out the reported parameters for different brands of salt. Fritz isn't on here, but you can find it on the company's website. A word of caution though. If you really want to dial it in, test your mix. The batch you get might vary from these numbers.

 

http://www.thatpetplace.com/salt-mix-guide

 

 

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[KenH]

I also had the same experience with using Kent while dosing causing some excessive precipitation issues on pumps and the glass.  Any of the salts like Kent or Red Sea Pro that mix to elevated levels can aggravate chemistry imbalance issues when dosing.  Holly is spot on when she said that it is generally best to use a salt that mixes closer to NSW levels like Fritz or the standard Red Sea (not the Pro) when dosing.

I personally would not worry about trying to elevate your alk much above 8.  It used to be popular to run up in the 10-12 dKH range, but if you look at most of the TOTM winners, the majority run their alk close to NSW levels.

In my own systems, I experimented with running alk at different ranges.  Color and vitality of the coral always seemed best if I kept things at around 8 with 9 being the upper limit. With higher alk, corals become more photosensitive and if nutrients run low and you have strong lighting you can sunburn your corals.

Here is a pretty interesting link where someone compiled the data from over 100 TOTM winners.  TOTM Data

[albertareef]

1 hour ago, KenH said:

I also had the same experience with using Kent while dosing causing some excessive precipitation issues on pumps and the glass.  Any of the salts like Kent or Red Sea Pro that mix to elevated levels can aggravate chemistry imbalance issues when dosing.  Holly is spot on when she said that it is generally best to use a salt that mixes closer to NSW levels like Fritz or the standard Red Sea (not the Pro) when dosing.

I personally would not worry about trying to elevate your alk much above 8.  It used to be popular to run up in the 10-12 dKH range, but if you look at most of the TOTM winners, the majority run their alk close to NSW levels.

In my own systems, I experimented with running alk at different ranges.  Color and vitality of the coral always seemed best if I kept things at around 8 with 9 being the upper limit. With higher alk, corals become more photosensitive and if nutrients run low and you have strong lighting you can sunburn your corals.

Here is a pretty interesting link where someone compiled the data from over 100 TOTM winners.  TOTM Data

Thanks for posting this Ken - pretty interesting data.  I think I only see one SPS tank that is running "high" Alk (11).  I also recall this being a "thing" for a while but seems the trend has drifted back toward levels more in line with natural salt water.

Interestingly, I have had an experience similar to Holly's with regard to calcium levels and Kent salt at target Alk although have, so far, avoided any precipitation issues.  I'm currently running 8.3-8.6 on Alk with fairly high (500) calcium as this is where it stabilized with my CA reactor dialed in.

As to the original question (uptake rate vs. Alk level) seems like there have been some good idea/advice/theories posted - wonder if there are any actual studies done on this?  Would be a bit tricky to do accurately I would think once you try and control for everything.  You would need to measure/track the biomass of the coral and keep the target Alk constant as well as figure out a way to measure uptake either directly (tracers?) or indirectly (replenishment rate).  Probably more work that anyone has been willing to dedicate.

[Willapa]

Thanks everyone! This forum is great! 

I use Kent and this was my next variable to rule out! I'll switch to Fritz and Jeff stocks it at a good price at CC.

I doubt I'll do a big water change, rather just switch with my normal water changes. So the effects will be slow. I'll report back if I have a major breakthrough.

Thanks again!

Trevor