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Aquarium Cooling Discussion from 6/30 meeting at the Crimson Reef

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Hi All,

We had a good discussion on aquarium cooling at our meeting at the Crimson Reef. Let's keep the discussion going in this thread.

Here are some of the main points we discussed:

1. Why prevent temperatures from getting too high?

- fish become stressed when oxygen levels decline in warm water

- corals can either bleach (they expel their symbionts as their symbiosis becomes unbalanced at high temps) or they undergo tissue necrosis due to bacterial disease (harmful bacteria are more pathogenic at higher temperatures).

2. What range of temperatures should we shoot for?

- most of us keep temperatures within a range of 78-82F. Some aquarists keeping organisms, like seahorses, that are especially sensitive to bacterial infections may keep temps as low as 74F.

3. How can we keep temperatures down?

- evaporative cooling with fans: This is the most economical solution. See below for links to a DIY aquarium fan solution. The downside to heavy reliance on fans is that you must watch salinity very closely. Most people using fans should use a good auto top-off system to keep salinity stable.

- An inexpensive temperature controller like an InkBird or a Ranco (more expensive) can be combined with fans and heaters to keep temperature constant.

- chillers: This is an effective solution, but can be noisy and expensive. It's also requires keeping an expensive back up chiller in storage in the case the main one fails. This is the only possible solution for folks keeping seahorses that require temperatures as low as 74F.

- emergency ice bottles: In case the power goes out and you cannot power your chiller or fan, have some frozen bottles of RO water available to drop into your tank. Frozen water bottles can bring temperatures down quickly and keep them low for a short time.

4. A DIY aquarium fan. The only brand of aquarium fan I have found to be reliable and effective is the German-made GHL fan. If you don't want to pay GHL prices, there is another option that I came across on the web (see this YouTube video for my source.)

For about $35 you can set up a quiet and powerful computer fan on your tank using a 3D printed mount and parts from Amazon.


Here's the fan


Here's the power supply


Here are the cables


Here is the 3D print STL for 8 mm glass. I am working on one that will be flexible for different thicknesses of glass. If you watch the video you can access the author's designs for other thicknesses of glass.


Here is a link to the InkBird controller that I usually use on my tanks.




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I was unable to attend the meeting but really wanted to hear the discussion about keeping temps down. So I’m extremely grateful for the meeting notes!

My reef is in a western facing room, and gets a fair amount of sun, the last few summers I saw tank temps in the low 80s, and was not very keen on it. I opted for the evaporative cooling option (with a cheap unit off amazon) and I’ve been very impressed with the results so far! The next few days will tell me if it’s sufficient. 

I set my apex up to turn them on at 78.5 and off at 78. Mostly because I wasn’t sure if they would keep up, I wanted to start them early. My Red Sea 250 it pulls down a half a degree in about an hour, that was with room temps about 75-77. 

I hope my anecdote is at least helpful enough for someone else to pursue the same route with success. I’m sure larger tanks, or less desirable environments require the chiller, but I think a lot of us can utilize the fans without making a huge investment!


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How's everyone doing with this weather? I see that the heat won't be over for a while... hopefully everyone is doing ok.  I have multiple tanks in a basement which gives me some advantage, though yesterday it was 78 down there. Didn't turn off the lights on the tanks, will today though. The classroom nano went up to 81 so I will need to set up one of those fans we learned about at the meeting, the tanks with controllers and fans stayed within .4 degrees of 78.5 which is how I set up the controller.

This is the controller I have been using on my 125, 72 bow and the classroom tank I maintain (brought it home for the summer):


I bought a few of these fans in 2017 to use in stands, one died after a couple years in the 125 stand but that's actually pretty good compared to anything else I have tried. Since then I remove the fan in winter and give it a good cleaning and check for rust, damage. Base has screw holes and it's mounted on the upper right side and blows lengthwise down the inside of the stand. Looks like right now it's only available as a 4 pack, that's probably a lifetime supply. Clamp on fans cost the same and rust, die after one season, and seem to get shoddier with every year.


I like to always have a spare controller, fan and probe (and return pump). They are cheap, and in my experience things only break when you don't have any time to deal with them. Probes last a year at least, sometimes multiple years. Usually not.


Those controllers also die if you let them sit in water. Duh. Oops.

For emergency aeration these battery powered pumps are great but not quiet, they are an old design. They take common D cell batteries that you can get anywhere, I prefer that to one with built in rechargeable batteries and they last many years as long as the batteries don't leak. They do not come with enough airline and you really need rigid tubing to get the air stone to the bottom where it will do the most good. These plug into the wall and if the power goes out senses it and turns on, or you can unplug it to turn it on. There are many cheap alternatives with more modern exteriors on amazon but they mostly don't plug into the wall, have built in batteries and they don't have great reviews. 


Good luck, hope everyone is keeping cool enough!



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For anyone following, my 65 gallon reef made the whole heat spell without ever breaking 78.5* room temperatures hovered in the high 70s but the house is air conditioned. The room is on the western wall of the house without any shade. 

The photo is the last 7 days worth of data for temperature. A couple mornings before the sun came around, it would actually cool below 78* occasionally. 


This is the fan I purchased, and I left it on the higher speed setting, and programmed the apex to turn it on at 78.5 and back off at 78. This may be a window that’s too tight, but with the little bit of bacterial stuff I’ve been seeing on my zoas, they’ve all seemed to bounce back after keeping the temperatures down!

Thank you again for posting about the discussion that was had! I feel more confident about the future of my reef now that I have this fan setup running. 


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