How To Keep a Fish Tank Cool

“An aquarium suffering from a spike in temperature has several visible signs,” Matt Hayes of Fish Shop Matt explains. They include:

• Cloudy or murky water, which happens due to increased bacterial activity (this is also a sign that the tank is cycling or the biological filter was disturbed).
• Fish gravitating toward aeration devices or the water’s surface and gasping

• Swimming erratically due to stress
• Loss of appetite due to increased water temperature
• Gasping for air or trying to gulp air near the surface of the water

Most importantly, watch the temperature. All tanks should have a thermometer that’s easily viewed.

While ideal temperatures vary by species, the key is knowing what’s best for your fish.

Hayes says, “Most tropical aquariums should sit in a temperature range between 75–80 F.” Many freshwater fish do well in 70–80 F water, but “with the thousands of fish available, it is always worth checking specific species and their temperature ranges.”

While mid to upper 70s are a good range for tropical freshwater fish, temperate fish like goldfish will be stressed above 75 F. Axolotls are even more heat-sensitive, and prefer temperatures below 70.

Todd Cecil, DVM, DABVP (Fish, Avian) explains that because most freshwater fish live in smaller bodies of water (lakes, ponds, and streams) that heat up and cool down in a wider temperature variance, they have a better ability to adapt.

However African cichlids from the rift lakes or Amazon river fish come from an environment with so much volume that temperatures do not fluctuate much.

On the other hand, the ocean’s size and temperature stability mean that saltwater fish rarely experience fluctuations of more than 2–3 F. Because of that, saltwater fish aren’t as adaptable and often exhibit heat stress sooner.

Cortisol, the body’s stress hormone, is great in small doses and helps a fish get out of danger. However, long-term stress increases the amount of cortisol in your fish’s system and affects the immune system, making them more likely to get sick or die.

In addition to the impact of stress, warmer water holds less oxygen. This is why fish will gasp near the surface when the temperature is too hot.

Cooling the water in your fish tank may require a multi-faceted approach that includes:

When you know the temperatures are heating up, close the blinds or curtains to reduce the amount of direct sunlight your aquarium receives.

Keep the room where your aquarium lives cooler—either with fans to increase circulation or air conditioning to maintain a cooler temperature.

All electrical equipment generates heat, some more than others. During the hottest parts of the day, turn off every nonessential piece of equipment, including lights if possible. Keep in mind that any equipment that creates surface water movement will help with cooling and oxygen exchange, so these should not be considered unnecessary.

One caveat is that plants and corals need to photosynthesize. If you have live plants or coral in your tank you’ll need to keep the lights on unless this is a short-term, heat-related emergency.

Aquarium fans can be especially helpful. Placing a fan near the water’s surface increases evaporation, which helps cool the tank by carrying away excess heat—often lowering the temperature by a few degrees.

Water bottles are readily available—just peel the label and freeze them. You can also try gel icepacks, but place them in a resealable bag in case one leaks. The contents can be toxic to fish.

However, don’t add too much ice in your tank. The temperature can drop too low, too quickly, says Dr. Cecil.

“With adequate circulation around your aquarium, the cooler water should be distributed,” says Hayes. And never turn your heater off because “if it does get too cold, the heater will kick in and bring the temperature back up.”

Aquarium chillers, like the JBJ Aquarium Arctica Titanium Chiller, are the most effective way of keeping your aquarium cool, but they’re pricey. If your aquarium is full of lots of cool-water fish, sensitive species, or expensive corals, a chiller is the best option.

Chillers come in various sizes to suit different aquariums and function much like a refrigerator. They need to be plumbed into your system and often need to be vented because of the heat they generate while working.

Increasing the air circulation around the tank will help dissipate heat and keep the temperature cooler. Move items away from the edges of your aquarium to give it more space.

If you can, open your aquarium’s lid and install a screen top to allow more heat to escape.

You can also experiment with different locations in your home—maybe it’s possible to place the tank next to an air conditioning vent or away from the wall.

Try lowering the water level or adjusting the placement of your aerators. If you can create more agitation at the water’s surface, you’ll increase the oxygen exchange rate and lower the temperature through evaporative cooling

A small but effective change is to adjust your feeding schedule. Fish often eat less during the hotter parts of the day and the food goes to waste, so pick a cooler time of day to feed them.

You can also reduce the amount of food for a few days while you’re getting the temperature under control. This helps minimize waste and keep water parameters more stable.

Evaporation from other cooling methods can be helpful —it gives you a chance to do a partial water change that helps lower the tank’s temperature. If you do this, try refrigerating the water for a little while—but don’t let it get cold enough to shock your fish. You don’t want the temperature to drop by more than a few degrees at once; this can lead to more stress-related health issues.

Add the water slowly, let it mix, and check the water temperature before adding more.

When things start heating up during the summer months, keep a close watch over your fish tank. Use digital thermometers and thermostats to track fluctuations, and set alerts for when temps get too high.

Floating aquarium plants, like water lettuce or duckweed, can help, especially if your aquarium is near a window.

You can also move larger decorations and rocks to the side of the tank closest to the window, allowing your fish more shade and a chance to cool off.

Every aquarium setup is a little different, so it may take some time to figure out what works best. However, by paying attention and taking quick action when the water starts to warm up, you can keep your aquarium water healthy and safe for your pets.