Warm weather can cause water temperature to increase to dangerous levels, in our experience most commonly kept fish species, including Coldwater fish can tolerate temperatures up to 29.5ºC (85ºF), without any short-term problems. Many hardier species can endure even warmer temperatures temporarily. Corals and other sensitive marine fish are most at risk from elevated temperatures, especially hard corals where we would suggest a maximum temperature of 28C (82.5ºF). Stability of all parameters is arguably more important than the exact level, providing extremes are avoided, this is especially true of temperature. A thermometer is an essential tool for monitoring water temperature.
Good oxygenation is vital in hot weather, as the water temperature increases the amount of dissolved oxygen decreases. In hot weather fish gasping at the surface is often a sign that oxygen levels have dropped dangerously low. Strong oxygenation is especially important if your aquarium is stocked to capacity, or with larger specimens. Adding an additional air pump during a heatwave can prevent the oxygen levels dropping too low.
Opening or removing your hood will help prevent overheating, as this will allow warm air to escape. Leaving the lights off can also make a considerable difference in reducing heat build-up, most fish, plants & even corals should survive a few days with a reduced amount of light.
Using a fan to circulate air across the surface of an aquarium will dissipate heat quickly as well as having a cooling effect due to evaporation. We stock aquarium cooling fans designed specifically for this purpose. We have found these to be very effective and can reduce the water temperature by several degrees.
Aquarium chillers are the best option for preventing overheating, They provide a stable temperature which is important to long term success, especially with marine species.