How To Protect Your Fish From The Summer Heat? 2021


With summer reaching its peak, many of use are feeling the heat!

Hot weather is often of great concern for aquariums too. While an aquarium heater will turn off when the temperature is above what it is set to, it cannot cool the water and therefore water temperature may rise above the optimum. Fortunately nearly all fish can tolerate periods of quite a high temperature with the majority able to withstand 30 to 32°C and some able to tolerate up to 40°C.

In an air-conditioned house, it is rare that an aquarium will heat up past 30°C, so steps to cool the water may not be necessary, but care must still be taken in hot weather. The reason for this is that warmer water holds considerably less oxygen than cooler water, so oxygen content drops as the temperature rises. Usually, it is low oxygen content rather than temperature itself that causes problems in hot weather.

If the tank is dirty or overstocked, even a slight temperature rise may cause the oxygen content to fall to a critical level. Therefore it is even more important to perform regular maintenance in warmer weather and to ensure your tank is in good condition. In particular, make sure that filtration is comfortably adequate for the tank size and load, that mechanical filter media is regularly cleaned and the gravel siphoned to remove detritus.

Be very careful with feeding as many fish eat less in warm weather and uneaten food will also pollute the water and cause oxygen depletion. Giving frozen rather than dry food is a good idea not just because it is cool and more tempting for the fish, but also because it is less likely to cause pollution if not all eaten.

To ensure good aeration you may also want to run an air pump during warmer weather, even if you do not do so normally. It certainly also doesn’t hurt to minimize heat build-up in the aquarium using the methods outlined below.

As mentioned, so long as the tank is well-maintained and not overcrowded, water temperatures up to around 32°C should not be a problem for most aquariums. However, if your house reaches temperatures greater than this, or if you are keeping more sensitive species, you may need to take steps to ensure the temperature does not go too high.

Some things you can do to minimize heat build-up are:

  • Turn off lighting during the day. Even fluorescent lights due produce some heat. In many cases, you can leave the lights off completely even for several days. If you have plants or coral that need light, run the lighting for the minimum time possible during the morning or evening.
  • Leave lids off or open slightly with a breeze directed across the water surface. Cooling by evaporation is quite effective. The water level may drop slightly as a result but rarely noticeably.
  • Perform a water change with cooler water. This also helps by ensuring the tank is clean and well-oxygenated. However, if the water from your tap is hotter than the tank there is little point. Let the tap run for a few minutes to get rid of hot water from the pipes.

If these steps fail to prevent the temperature from increasing you can lower the water temperature by adding a little ice or floating a bottle or bag of ice in the tank. However, this is only recommended as a last resort as it can decrease the temperature quite quickly, which may be even more stressful for the fish than a temperature that is slightly too high.

If your house regularly reaches temperatures above which your fish can tolerate, especially if you are keeping very temperature-sensitive species, you may need to invest in an aquarium chiller. Water is pumped through the chiller which is thermostatically controlled and refrigerates water to the desired temperature. Unfortunately, chillers are relatively expensive, but they are the only reliable way to maintain an ongoing steady water temperature cooler than the ambient temperature.

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