Managing Tank Temperature with an Aquarium Heater or Chiller

Fish depend on their environment for their comfort and well-being. Their body temperature varies according to the water temperature around them. If the water is too hot or too cold, it can lower their resistance to illness. Then they get sick from parasites like ick.

Marine invertebrates like corals have the same challenge. If the water temperature is too high, coral will bleach white, then die. This unfortunate circumstance happens all around the world’s oceans.

Some species like goldfish can handle a wide temperature range from 40 to 80 degrees F. It doesn’t mean they enjoy that full range, but it won’t kill them, at least. Others like the tropical fish tiger barbs need 76 to 80 degrees constantly.

It’s not hard to achieve the perfect temperature zone for your tank. The first step is to use a reliable thermometer. Monitor the tank for a couple of days and see what the temperature averages are. Then you’ll know if you need an aquarium heater or a chiller.

In some cases, you might need both pieces of equipment. For example, in the wintertime, if air in your home hovers around 68 degrees, chances are the tank water will be lower than that. But in the summer, you might need a chiller to lower the temperature.

Other factors affect the environment inside the aquarium, too. Lights, filters, and pumps might raise the temperature. Water changes can throw off the balance. Even where you place the heater or chiller in relation to the pump or filter is important. It has an impact on how well the cooled or heated water circulates inside the tank.

Aquarium heaters

When you choose an aquarium heater, plan on at least 100 watts for a 20-gallon tank, or 5 watts per gallon of water. That’s because small aquariums lose heat faster than large ones. Also, err on the side of safety if you place the tank in a cold room. It’s better to have more power than you need as long as you can adjust the temperature.

Heaters aren’t very expensive, but they are worth the investment because there is no other safe and consistent way to warm up aquarium water.

Aquarium chillers

When the aquarium water is too hot, you’ll need a chiller. If you see your fish are struggling to breathe, it might be because they are too warm and can’t get enough oxygen from the water.

You can create a temporary chiller with a fan or by using small bottles with ice inside. But if you have a reef aquarium, you need a permanent solution. Some chillers consist of cooling coils inside the tank. Others pull out water, cool it, then pump it back inside. Either way, a chiller is essential if you want a healthy environment for your coral.


No matter which solution you use to manage water temperature, test it ahead of time. Set up the tank with the chiller or heater plus a thermometer. Then let it run for a couple of days to see if the temperatures stay comfortable for your aquarium’s inhabitants.

Check out our reviews of the best chillers and heaters for aquariums. They will help you select the right one for your setup.