Aquarium chillers are devices that reduce the temperature of the water in a fish tank. At first glance, an aquarium chiller may appear to be an odd accessory for a tropical aquarium. They are, after all, filled with tropical animals that are accustomed to tropical temperatures.

While tropical fish need warm water, real problems can arise if the water gets too hot or fluctuates too much. As the temperature rises the oxygen level drops, making it more difficult for fish to breathe. Higher temperatures also lead to increased problems with nuisance algae and parasites. Most importantly, tropical fish like stability. High temperature fluctuations often lead to unhealthy fish.

This is especially true for a saltwater aquarium.

Day to day temperatures in the ocean are very stable. However, achieving stable temperatures in a reef aquarium can be very difficult. All of the equipment used to maintain a reef tank, like high intensity lighting and powerful pumps, put a lot of heat into the water. This can make the tank heat up rapidly. During the summer, the heat can become lethal. While fans may help some, many aquariums need a chiller to keep temperatures safe and steady.


Do not buy an underpowered chiller. Keep in mind that most aquarium chillers are rated for the volume of water they can cool, but do not take into account heat put into the aquarium by lights and pumps. So, if you have a 100 gallon aquarium, you will need a chiller rated for more than 100 gallons.

When picking a chiller, consider the long term costs. If you buy a chiller that is just powerful enough, you may save some money initially, but you will pay far more in the long run. A chiller should not run more than 15-20 minutes each hour. However, an underpowered chiller will run a lot. This will shorten the life of the chiller and raise your electricity bill considerably. You can get an estimate of your electricity usage using our free Aquarium Electrical Cost Analysis Calculator.


Most chillers are not works of modern art. But, hiding the chiller in an enclosed area like the aquarium stand isn’t wise unless the stand is well ventilated. As the chiller draws heat out of the aquarium, it needs to expel that heat into the environment. If the chiller is not well-ventilated, heat will build up. This will cause the chiller to work less efficiently.

Some aquarists place the chiller in a separate room (or the garage). This takes extra work, but can hide an unsightly chiller. When I installed my chiller next to the stand, I put an end table over the chiller and disguised it with a thin tablecloth. This kept the chiller well-ventilated and my wife happy.

You also want to consider the amount of power the chiller uses. Chillers pull a lot of electricity, so you probably don’t want your chiller plugged into a multi-plug adapter. You also need to be careful, because if your chiller, combined with your other equipment, is drawing more power than the circuit is built for, the circuit might trip causing power to be lost. This can be dangerous if it happens while you are away.


There are two basic types of chillers: drop-in chillers and in-line chillers. A drop-in chiller has a heat exchange coil that is placed in the sump. This is pretty straightforward, so we will focus our attention on installing an inline chiller.

Inline chillers must have water pushed through them. Before installing your chiller, you need to determine the appropriate flow rate, which should be listed in the manual. If the water is moving too fast or too slow, the chiller will not work properly.

Nano-Tank Chillers

You will (probably) need:

Most nano-tanks have a dedicated reservoir in the back of the tank that houses all of the filtration. The best way to install a chiller is to insert a feed pump into the reservoir (or the main tank if there is no other option). A Maxi-Jet pump will usually fit in the space allotted. Attach the U-tube with hose clamp to the pump and drop it into the reservoir. Then, run tubing from the feed pump to the inlet of the chiller. JBJ makes a nano chiller installation kit that includes many of the parts you will need. Next, run tubing from the outlet of the chiller back to the tank. Attach the tubing to the S-tube which will hang on the back of the tank.

Double check to make sure everything is snug and that you have created drip loops, and fire the pump up. Then, jump ahead in the article to "Temperature Controllers."

Chillers for Larger Systems

You will (probably) need:

For this installation guide, we will assume that your chiller is next to the stand, and that you have a sump. You have two main options for feeding the chiller. If the flow rate on your return pump matches what the chiller needs, you may want to plumb the chiller into the return line. This means that the return pump sitting in your sump will deliver water to your chiller, and then directly from the chiller back into the aquarium.

Your other option is to have a dedicated feed pump sitting in the sump. Some aquarists prefer this setup. There are a few advantages to this. Water from the sump is not slowed down going through the chiller, affecting tank circulation. Nor will water sit in the chiller whenever the return pump is turned off. Standing water can easily freeze inside a chiller, which can cause significant damage. The downside is that you will need an additional pump.

Installing a chiller on a larger aquarium is not much different than the nano-chiller installation above. If you are using the return pump, insert the chiller inline between the pump and the return nozzle. If you are using a feed pump, send tubing to the inlet of the chiller and then from the outlet back to the sump.


The temperature controller measures the temperature of the water to determine when the chiller should run. Many chillers have internal controllers. But, you can also purchase an external temperature controller or use an aquarium controller like the Reefkeeper or Apex.

The best temperature controllers are dual stage. This means that they can control two devices at once: the chiller and the heater. The last thing you want to do is have your chiller and heater running at the same time.

Set the temperature controller to turn the chiller on when the tank reaches a target temperature, say 80°. Many controllers then allow you to set a temperature to turn the chiller off at. Set this a few tenths of a degree below the temperature the chiller kicked in at, say 79.5°. This way, the chiller will not constantly turn on and off. Set your heater to come on at a lower temperature, say 79°. This way, your heater and chiller will not be in competition, and your aquarium will not fluctuate more than 1°.

There you have it! You now have a functioning chiller that is keeping your fish safe and happy.

Now, don’t forget periodic maintenance. Check the chiller fan and housing often for dust buildup to keep the air flowing. A chiller choked by dust will run inefficiently and may break down. Occasionally, remove the chiller from the system and run a vinegar/water solution through the chiller to remove any calcium buildup. A bucket, pump, and some tubing work great for this task.

If you have any questions about choosing or installing a chiller, we would be happy to assist you.

See how an aquarium chiller works in this diagram