As the long days of summer begin and the mercury inches up the thermometer, sometimes it’s all too easy to enjoy the sunshine and forget about the effects of the heat on your aquarium fish. To ensure your fish’s health, both freshwater aquariums and saltwater aquariums need to stay below a maximum of 86 ° Fahrenheit. However, the water temperature in your custom aquarium can increase during these hot summer months without you realizing it.

Why Heat is Bad for Aquarium Fish

If you find that the water in your aquarium is getting warm, don’t be too alarmed. Remember that unlike custom aquariums, there are no magic heaters in the wild to ensure that a fish’s water temperature remains constant. Cold winter nights, hot summer days and weather like rain all work together to ensure that fish in their natural environment do not experience the same temperature for too long. Most natural aquatic environments can vary up to 30 degrees throughout the day and night.

However, because oceans, rivers, and lakes contain so much water, it takes a long time for the temperature to rise or drop. In a custom aquarium, there is not nearly as much water, so it can quickly get hotter or colder based on the outside temperature. It is this rapid change in temperature that causes issues.

The other main killer of aquarium fish due to heat is the lack of oxygen dissolved in the water at higher temperature levels. When the water temperature in your aquarium rises, oxygen levels in the water drop. Your fish can become not only overheated but also starved for oxygen. If you’re finding your aquarium fish gasping at the surface, it’s definitely time to start cooling your aquarium! There are plenty of easy ways to keep things cool and keep your fish happy on a hot summer day. There are also plenty of things NOT to do, that could end up harming your aquarium fish instead. So here are a few do’s and don’ts in keeping your tank’s temperature down when the weather heats up:

DO: Keep the Room Cool

The best and easiest way to keep your custom aquarium cool is to keep the rest of the room cool as well. For example, if your tank is standing in direct sunlight for much of the day, you can block the sunlight by drawing the blinds or curtains. This has the added benefit of reducing excessive algae growth. Also consider leaving the air conditioning on, or having fans blowing. In fact, simply placing a fan so it blows directly across the water can make a big difference in water temperature.

DON’T: Directly Add Cold Water or Ice

Naturally, one would think that the best way to cool down water is to add ice or cold water. However, it is not a good idea to simply add ice to a fish tank. The water in most saltwater and freshwater aquariums has been specially treated. The water or ice you add is not treated. This could drastically change the chemical composition of the water, and this change will stress a fish more than temperature changes! Also, if you suddenly add ice to an overheating aquarium the temperature will decline very rapidly. This shock of suddenly colder water can cause immense stress, which makes fish vulnerable to disease and can even cause immediate death.

DO: Use Ice Bottles to Help Keep Things Cool

You can add plastic bottles of frozen water to help cool things off. Take extra care that you don’t overfill the bottles, and clean the outside thoroughly. Make sure they do not crack or otherwise leak untreated water into your treated tank. Use smaller bottles to keep the tank from cooling too quickly. A good idea is to place an external aquarium filter in a bucket and pack the bucket with ice. This will cool the water as it passes through the filter without anything foreign going inside the actual tank. You can also route the filter pipes and hoses through the bucket to help further cool the water.

DON’T: Turn Off Your Aquarium Heater

It seems like it would be a good idea. But the problem with turning off the heater in a custom aquarium is that most heaters will only turn themselves on if there is a drop in temperature. So you gain nothing if you turn off the heater when it is already hot outside. In addition, if you forget to turn the heater back on again, it won’t be able to warm your aquarium fish when the temperature drops off rapidly at night. It’s a better idea to just leave it on, rather than risk potential problems later.

DO: Turn off The Aquarium Lights

Many aquarium lights tend to generate a lot of excess heat. This is especially true for metal halide, or T5 lights. So, if your aquatic plants allow it, you can keep your aquarium lights on for only a few hours. If possible, keeping the lights off entirely during the hottest days of summer can definitely help keep air and water temperatures down.

DO: Open the Aquarium’s Hood

A quick and easy way to reduce the temperature inside your tank is to open or remove the top hood. This helps the heat escape. Beware if your fish are ‘jumpers‘, however. If you are not careful, you may find them trying to ‘surf the floor’! You also want to ensure animals such as cats cannot gain access to the tank. A mesh top for your tank is a great idea that not only keeps your tank cooler, but also keeps prying paws out of your custom aquarium.

A Cool Aquarium Fish is a Happy Aquarium Fish

No matter which method you use, the key is to be sure to keep the rate of change slow. A rapid change in water temperature can be harmful to your aquarium fish, and the tank in general. Therefore, it’s a good idea to monitor your aquarium’s water temperature if it gets too warm outside. It’s better to work to maintain the tank’s temperature, rather than have to find a way to cool it off after it overheats. However, if you’re in doubt, the best thing you can do is speak to your professional aquarium maintenance specialist. They can help you find the best solution to ensure your custom aquarium always runs at its optimal temperature.