Reef Tank Temperature – Everything You Need to Know

Keeping a reef tank can be a challenge but learning how to take care of it is extremely rewarding. Something that a lot of new reef tank owners have questions about is reef tank temperature. A lot of people think that the most important thing is keeping the water warm enough, but there’s actually a lot more to it than that.

When it comes to reef tanks, maintaining an appropriate temperature is essential, but preventing temperature fluctuations is important, too. Let’s take a look at why a stable temperature matters and what you can do to get it right.

Why Temperature Matters

Every living thing in your aquarium is sensitive to temperature fluctuations, but some are more so than others. Coral is exceptionally delicate and can bleach or die if exposed to temperature swings of more than two degrees in 24 hours.

Temperature fluctuations of several degrees can be disastrous to any aquarium, but reef tanks need special care. Most people feel that the ideal temperature for most reef tanks is between 76 and 79 degrees F (24 – 26°C). That said, some people recommend going as high as 89 degrees F (32°C).

So, what is the best temperature for a reef tank? One way to know for sure is to research the origin of your coral and learn as much as you can about its natural environment. Remember, you’re trying to get your tank as close to natural as possible, so go with whatever temperature the coral is used to.

If you’re still not sure or if you need more clarification, it’s a good idea to ask the merchant that is selling you the coral where it came from and what they recommend.

Tank Size

Tank size has a significant effect on temperature stability. The larger the tank, the less the temperature fluctuates. Why? Because it takes longer for large volumes of water to gain or lose heat. That’s why when you go into the ocean at night when the air is cooler, the water is still warm from the heat of the day.

Here’s an example. Let’s say you have a 20-gallon tank and a 100-gallon tank. At night, you turn the lights off. In the morning, the temperature fluctuation in the 20-gallon tank will be much greater than that in the 100-gallon tank.

What Kind of Heater is Best?

Submersible heaters are effective but tend to heat the water unevenly. The area close to the heater gets warm, but you have to rely on movement to circulate the warm water and keep the temperature even.

Most people find that inline heaters are a better option because they’re more efficient and heat water more evenly. Ultimately, the heater you choose comes down to personal preference, but an inline heater is usually a little less work.

What Can Happen if the Water Is too Hot?

One serious problem that can occur when water temperatures are too high is that it won’t hold enough oxygen. Every organism in your tank relies on having enough oxygen to survive, so this can be a pretty big deal. If the problem is severe, it can be catastrophic.

Research the fish that you’re planning to have in your tank to make sure they have the setup they need. Most fish that live close to coral reefs in nature like a higher oxygen content as the crashing waves aerate the surface.

Higher water temperatures also increase the decomposition rate of debris and the rate of bacteria reproduction. Bacteria also consume oxygen, so if there are too many bacteria, the oxygen content suffers as well.

What to Do if Your Tank is Too Hot

If your reef tank is too cold, you can easily adjust the heater to slowly raise the temperature. When your tank is too hot, though, the problem is a little trickier. That said, there are a few things you can try.

It’s generally not a good idea to have a reef tank (or any aquarium, really) next to a window where it is exposed to direct sunlight. That said, we know you don’t always have a choice, depending on the setup of your home and where you have space to place the tank.

If your reef tank is by a window and gets direct sunlight for part of the day, close the blinds or hang something to block the sun. This also helps prevent algae growth as algae thrive in sunlight and warm temperatures.

One of the easiest things you can do to keep your reef tank from getting too hot is to keep your air conditioner running. This is a great way to keep the ambient temperature cool which goes a long way to keep your tank from getting too hot.

If you aren’t lucky enough to have central air, think about getting a unit for the room where your reef tank is located. It’s one of the best things you can do to control the heat in the summer.

Another option is to place fans inside the hood of the tank. Some people even fit computer cooling fans into the hood, aiming the air across the surface of the water to help remove the rising heat. You may find that running a fan in the cabinet with the equipment helps, too.

If you aren’t having problems with fluctuations but rather your reef tank temperature is consistently too high, the problem might be your lights, especially if you have metal halide lights as they tend to get really hot.

In this case, consider turning your lights off for longer lengths of time during the day or invest in lighting that won’t have as big an effect on the water temperature.

Use a Chiller

If you tried all the simple fixes but can’t seem to get it right, you may have to invest in a tank chiller. This is the most expensive solution, but, in some cases, it’s the only one that works.

There are two kinds of chillers, drop-in and in-line. Drop-in chillers work in the sump pump while in-line chillers cool the water before it passes into the sump pump.

Drop-ins are a little easier to install, but in-line chillers can be set up away from the tank and connected with tubes and hoses. This comes in really handy if you’re working with limited space. You can place them anywhere you have room as long as you have the right tubing to connect them to the system.

When using a chiller, you also need to invest in a temperature controller. You can get a single-stage model if you just want something to use with the chiller or a dual-stage controller that controls both the chiller and heater.

The Right Reef Tank Temperature Makes All the Difference

Maintaining a reef tank is a challenge, but the rewards are well worth it in the end. Remember, you’re essentially setting up a mini-ocean environment in your home, and the best temperature is a consistent one.

Ideally, your tank temperature shouldn’t fluctuate much more than two degrees in 24 hours. If the temperature changes too much too often, it will stress your tank and cause problems for your coral.

Research the natural environment of your coral, so you know for sure what the best temperature setting is. In most cases, it’s between 76 and 79 degrees F (24 – 26°C), but it can be as high as 89 degrees F (32°C). If you need help, talk to the person selling you the coral about its origins and what they recommend.

Check the water temperature often and make changes when needed to be sure your tank stays healthy and beautiful.