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.