5 Easy Methods for Cooling Aquarium Water During a Heat Wave

During the hot weather seasons when heat waves hit, you may struggle to keep your aquarium water cold enough for goldfish, goodeid livebearers, axolotls, and other cool water species. While it is relatively affordable to warm up the water with a heater, it can be much more expensive to buy equipment that reliably cools down the temperature. One simple tool to start with would be some kind of digital thermometer with an alarm that beeps if the water gets too hot (or cold). Then you know when it’s time to try one or several of these five techniques to lower the temperature and help your animals get through the summer.

1. Remove Heat Sources

The easiest method is to remove all unnecessary equipment — such as the heater, UV sterilizer, skimmer, and even hot lights. All of these devices use wattages of power and become sources of unwanted heat in the tank. In terms of lighting, consider switching to an LED light if you haven’t already because they tend to produce less warmth compared to other types of lighting. Also, a sponge filter that runs off a simple air pump may produce less heat compared to a powerful canister filter.

The Easy Plant LED is designed to be cooler than other lights.

2. Change Locations

If your aquarium is exposed to direct sunlight throughout the day, consider moving it to a cooler, shaded area of your home. Even indirect sunlight can increase the temperature, so if your tank is in a room with lots of windows, keep the curtains closed during the daytime if at all possible. Besides sunlight, sources of hot air can also have a big effect on your fish tank, so move your aquarium away from any heating vents or exterior doors that let in hot air from outside every time they are opened. Appliances — such as an oven, dryer, or even a gaming console blowing out hot air — can also give off lots of heat.

In cases where the aquariums are in a rack or shelving system, put your cool water fish in the bottom-most tanks. Because heat rises, the difference in temperature between the top-most and bottom-most fish tanks can vary by several degrees, so we want to take every advantage possible. In fact, many people keep their axolotls in the basement where it’s cooler year-round because all of the conditioned air sinks down there while the warm air rises to upper floors.

Close the curtains to help reduce heat.

3. Use Evaporative Cooling

You know how when your body is hot, it starts pouring sweat, which then evaporates to cool you down? This evaporative cooling process occurs when water evaporates into the air as a gas and uses up energy (or heat) from the surrounding area. By encouraging evaporation in an aquarium, it will use up some heat in the water and decrease the temperature by a few degrees. The first tip is to remove the tank lid so that water can evaporate more easily and heat can escape. If you are afraid of animals escaping the aquarium, go to a local or online store that sells mesh lids for saltwater tanks. You can also lower the tank’s water level by a few inches so it’s harder for jumpers to make it out.

If passive evaporative cooling is not enough, increase surface agitation to speed up evaporation. An easy way is to add an air stone or sponge filter because the popping bubbles cause surface agitation and encourage gas exchange. Many hobbyists forget that in the summer, warm water holds less dissolved oxygen than cool water, so adding turbulence at the surface can minimize the risk of oxygen depletion.

In the past, we have also used a portable, ultra quiet USB fan with an adjustable neck so that the air flow is aimed directly at the water surface for maximum effect. The fan was connected to a small USB battery pack that can provide electricity during a power outage. Then the battery pack was mounted to the wall just above the tank using strong Command strips, and the whole unit was charged by using a long extension cord plugged into a wall outlet. If this DIY setup is not very attractive to you, you can always use a table fan or ceiling fan to cool the whole room, but it may be louder in volume or not as effective because of the distance.

USB fan with battery pack

4. Add Insulation

After working so hard to reduce the temperature with evaporative cooling, it would be counterproductive if heat from the surrounding environment continued to permeate into the aquarium water. Therefore, as a defensive tactic, we can cover the back and two side walls of the tank with insulation to keep in the cold. (In the case of a severe heat wave, the front panel can also be covered.) Some aquarists like to use sheets of Styrofoam, whereas we have personally used double reflective insulation. This foil-colored bubble wrap is easy to cut to the right size with just a pair of scissors, and its light weight allows you to attach it to the upper and lower rims with ordinary Scotch tape. We’ve successfully used this technique to help prevent heat from entering the tank as quickly and drop the temperature by a few degrees.

Double bubble reflective foil insulation

5. Buy a Chiller

If none of the previous methods worked, then the most reliable solution is to save up and buy a chiller. This electronic device works much like a canister filter where you have a box-shaped machine sitting outside of the tank with two hoses that reach into the aquarium. One hose brings water out of the tank into the chiller, and the other hose sends the cooled water back into the tank. Despite the fantastic results, we waited till the end to mention chillers because a single unit can run about several hundred to over $1000, depending on the size of your aquarium. If you decide to go this route, do your research to find the best brand and model that works for your budget.

Aquarium chiller

Can ice be used to cool down aquarium water? This method involves freezing bottles of water (or putting reusable cold packs inside a Ziploc bag) and floating them inside the tank. We have tried this technique before in emergency situations, and it is quite time-intensive. The ice melts very quickly, so you must constantly replace it and refreeze the bottles. Plus, the temperature in the aquarium becomes extremely volatile, which can be quite stressful for the fish. Another similar method is to do water changes with cooler water, but this assumes that your tap water is even cold at all, which may not be the case during the hottest days of summer. The previously mentioned tips in this article are more consistent and do not cause drastic temperature swings, which is best for your fish’s health.

Thankfully, some fish actually like higher-than-normal temperatures, so if you live in a perpetually hot climate, check out our top 7 warm water species that aren’t afraid of a little heat. Enjoy nature daily!