How to stop a tank from overheating


One of our readers asks expert Jeremy Gay how to avoid his reef tank heater from overheating the water...

Q) Yesterday I awoke to find my reef tank at 33°C with a lot of unhappy fish and corals. I switched the heater off and quickly did a small water change to bring the temperature down a bit before I went to work, and then left it to cool gradually. By the time I returned home it had returned to its normal temperature of 26°C. I inspected the heater, and it was definitely the culprit as it looked burnt. My fish and some of the corals are looking a lot better than they were, but the pulsing Xenia seems to have taken the worst hit. Is it likely to recover, seeing as how it looks at the moment? How can I stop this type of thing happening again in the future?


A) Jeremy responds: Many marine keepers now use separate titanium heaters and temperature controllers. Digital controllers can not only shut off a heater if it gets too warm, but you can also plug in a cooling fan and that will kick in at your desired upper limit, like 27°C for example. Or, if you have the budget, invest in a cooler which also heats. They are expensive but super-accurate and you'll have the ultimate in temperature control.

An aquarium controller like Apex or a Seneye will alert you on your phone if the tank is getting too hot, and the Apex can even turn devices off when you're not there. Failing that, just invest in as expensive a heater as you can afford (as its components should be more reliable) or better still buy two low-powered models which will heat the tank less slowly if one fails in the ‘on’ position.

As far as the Xenia goes, they are one of the most heat tolerant corals going, so it should survive the hot spell; its appearance should begin to improve soon.

Coping with a sudden heat crisis

If an aquarium overheats, either due to a heater malfunction, or a summer heatwave, don’t be tempted to carry out large water changes to cool it down. Sudden temperature changes represent a danger to your fish — possibly even a greater one than a tank that’s too warm. Instead, switch off the lights, open the hood and let it cool down naturally. If it’s so overheated that you feel you must do a water change, stick to no more than 20% and aim to just drop the temperature by a couple of degrees rather than use very cold water. Adding aeration by way of an airpump and airstone will also help increase oxygen levels, which will be affected by the warmer conditions.