Guide to Maintaining The Ideal Aquarium Temperature (2024)

Long gone are the days of putting a betta in a fishbowl on the counter in tap water and calling it a day.

There are a lot of valid concerns when getting new fish or starting a new tank. A common question people ask is, what water temperature does my fish need?

Thankfully, it’s not rocket science, even with a mix of different species of fish, inverts, corals, or even plants. There is usually a safe range that is easy to maintain.

Why is Temperature Important?

Every animal has its limits for either hot or cold temperatures. Humans and mammals have greater temperature tolerances because we are endothermic, or warm-blooded. Humans are also able to use outside sources to moderate our temperature, such as a jacket or winter boots.

Fish, on the other hand, are ectothermic, or cold-blooded. Cold-blooded means the temperature of their surrounding water regulates their internal body temperature.

Extreme temperature fluctuations can cause unnecessary stress on your fish and even lead to death. Not to fear, temperature is both easy to test and adjust!

Risk of High Temp

Usually, when we think of temperature issues in an aquarium, we consider acquiring a heater to help maintain water temperature. However, certain fish and invertebrate species require lower water temperatures.

In higher temperatures, less oxygen is dissolved in the water. To make matters worse, it increases the metabolic rate for fish. This means that they should be intaking even more oxygen!

An unnaturally high temperature will leave your fish gasping for oxygen and will lead to stress-born illnesses, such as ich!

Risk of Low Temp

In low temperatures, your fish’s metabolic rate comes to a stall; this has more consequences than just a slow fish.

The lowering of their metabolic rate causes fish to lose their appetite. This creates unnecessary stress and compromises the immune system of your fish!

Best Temperature Range

Different species of fish and inverts have different tolerances for temperature ranges. This usually directly correlates with the temperatures of the body of waters which they are native!

Listed below are common fish to keep in aquariums and their ideal temperature ranges. Keep in mind these ranges can offer what seems like a fair amount of wiggle room, but ideally, the temperature in your tank should be kept consistent.

Freshwater Species Temperature Range

Saltwater Species Temperature Range

Coldwater Species Temperature Range

Certain tank mates prefer cold water. If you’re interested in keeping a cold water tank or seeing what you could possibly keep with your goldfish.

Explore the list below:

Tropical Species Temperature Range

You might’ve heard someone refer to tropical fish, and might be thinking I wonder what temperature range a tropical species prefers.

Tropical fish often need a temperature between 75 to 80 degrees Fahrenheit. Most fresh and saltwater fish sold in pet stores prefer these temperature ranges, with the exception of coldwater fish.

How to Control The Water Temperature

There are a couple of different ways to help control the temperature in your aquarium.

First, make sure to invest in a thermometer so that you can keep track of the temperature in your aquarium. These are often inexpensive and submersible.

Tropical Tanks

If you need to keep water warmer, buying an aquarium heater is going to be your best bet.

Place your aquarium heater where there is ample water movement. For example, you can place them by outputs, powerheads, filters, or air-stones. This placement ensures the water stays at a consistent temperature throughout the tank.

Depending on the size of the aquarium, you may need heaters of greater or lesser strength. In some large aquariums, you may need multiple heaters placed throughout the tank.

These submersible aquarium heaters are sold with application suggestions based on the size of your aquarium. However, a heater does not necessarily automatically get your tank to the desired temperature. For better temperature control, you may want to pick up a heater with temperature settings.

Coldwater Tanks

For fish and invertebrates that require colder tanks, chillers are available for purchase. Chillers are typically kept outside of the aquarium.

Chillers are more expensive than heaters, but they’re reliable. A cheaper alternative to cooling your water is floating ice packs on the top of the tank. However, this is far less convenient. Make sure to remove these after the ice pack is warm.

Another method for keeping your aquarium cool is taking off the lid, just make sure your fish are not prone to jumping. Also, if you have cats, it’s probably best if you don’t do this.

Turning off the light will also decrease the temperature, as it introduces heat into the tank.

Causes of Unnatural Temperature Change

Tank Location

Location, location, location! So we might not be talking about real estate, but the area of your aquarium is essential for the comfort and safety of your fish.

One of the most common mistakes is placing your aquarium near a window. Windows allow sunlight into the aquarium which will raise the temperature of the aquarium. This type of placement will also lead to algal blooms and unnecessary stress on your fish during the summer months.

Another poor location is near an air conditioning unit, fan, or heater. It might seem like you’re skipping a step by cooling or heating your tank using the same tools you use in your home. However, this will just cause unnecessary temperature fluctuations in the tank and it will not evenly distribute the temperature throughout the tank.

The best location for your tank is an area of low sunlight with a consistent temperature.

Faulty Aquarium Heater

The best way to tell if you have a faulty aquarium heater is to have a submersible thermometer in your aquarium.

Aquarium heaters work overtime in your tank. Therefore, they run the risk of malfunctioning after extended use. Like many pieces of electronic equipment, you also run the risk of purchasing a faulty device right off the bat.

If you believe your aquarium heater is not heating the water, test it in a smaller container or aquarium of water. It should take approximately a day to be able to see a rise in temperature in your aquarium.

Water Changes

A common mistake made when performing regular water changes is not unplugging your heater. If you don’t unplug your heater while it’s out of the water, you put unnecessary strain on it. This is an easy way to kill a heater over time.

When performing water changes, try to get the replacement water’s temperature as close to the temperature in the tank. For tanks that need significant water changes, this may involve using a water heater or chiller to prepare the water for the change.

Don’t add warm or cold water to try to lower or raise the temperature of your tank. Changing the temperature of your water should be done gradually. This way you’ll avoid shocking the tank.

Additional Fish

When acclimating a fish to a new tank, it’s important to check that certain water parameters are as close as possible to the water that they were previously living in.

One of the simplest methods is to allow a fish to float on the top of the tank for approximately 30 minutes to adjust to the temperature of your tank. This method works best for freshwater fish.

Saltwater fish need to be acclimated to the temperature as well, but they also require extra acclimation to the pH and salinity of the water. Saltwater acclimation is best accomplished using a drip acclimation.

Additionally, when adding new fish to an aquarium, make sure they have compatible temperature ranges. A consistent temperature will increase the longevity and health of your tank mates.

How to Safely Correct the Water Temperature

The best way to safely correct the temperature of your water? Slowly.

Fish often face fluctuations in water temperature in their natural habitat, but it happens slowly due to the large amount of water available.

All the methods recommended above for cooling and heating a tank will gradually alter the temperature of your aquarium.

What about Coral and Plants?

Corals

Different corals come from diverse regions and require different temperatures to thrive in your aquarium. Most corals require higher temperature ranges, approximately 75-78 degrees Fahrenheit, although some corals prefer even warmer waters.

If your water is too hot or your lights are adding too much heat to the tank, you may see bleaching on your stony corals. Coral bleaching can be fixed by changing the position of the coral in the tank if the temperature ranges are in the coral’s parameters.

There are cold-water corals that reside in waters with temperatures below 40 degrees Fahrenheit! Yikes! These are rarely sold, though, and are not compatible with many of the tropical fish species sold online and in stores.

Aquatic plants

Aquatic plant’s ideal temperature ranges from 70-80 degrees Fahrenheit. These are, of course, going to need cooler or warmer temperatures according to the area of the world they reside in.

If you’re looking for plants to go into a colder water tank, There are a couple of aquatic plant species that do well in colder water temperatures including:

• Java Moss (wide range: 59-86 degrees Fahrenheit)
• Marino Moss Balls
• Cabomba
• Water Cabbage
• Brazillian Pennywort
• Java Fern

Final Tips

Appropriate temperature is important for the health of your aquarium.

Remember:

• Your fish need a steady (and appropriate) temperature in their tank.
• Keep a thermometer inside the tank, so you catch temperature fluctuations before they stress or cause harm to your tank.
• Select fish that have compatible temperature requirements
• Use a heater or a chiller to control your water temperature
• Always raise or lower water temperature gradually

Follow these tips and you’ll be well on your way to success. Good luck and thanks for the read!

Read more fish tank maintenance guides:

• How to remove brown algae from your tank