Aquarium Chiller - Water Chiller

Updated August 12, 2019
Author: Mike - FishLore Admin
Social Media: FishLore on Social Media

As the aquarium hobby continues to advance more gadgets are making their way into the market for hobbyists. The aquarium chiller or water chiller has been around for some time now but chillers are slowly starting to become more affordable for your average aquarist. Many are starting to get into saltwater reef tanks and this side of the hobby seems to be growing rapidly. Reef tanks are primarily geared towards coral keeping and these corals often times require intense lighting. This lighting is usually supplied by metal halides, VHO fluorescents, T5 fluorescents or compact fluorescent lighting.

aquarium chiller

It's fantastic that we are able to use these ligthing fixtures to get the necessary light over these light loving corals, but there is a downside. The aquarium water temperature will often start to creep up into the mid to high 80's °F (high 20's - low 30's °C), sometimes even the low 90's °F. While natural reefs can be in the mid to low 80's °F they don't have the temperature swings as often and as extreme as the swings in the home aquarium.

For instance, when the lights are off, the tank temp will probably hover around the mid 70's °F. Obviously the temperature of the room the tank is located in will have an effect on the tank temperature. But, once they main lights come on in the morning the tank temperature will slowly start to climb to possibly uncomfortable levels in the afternoon. It's this swing from the lower temps to higher temps that could be cause for concern. Particularly if you're keeping corals and sensitive species of fish or other inverts. Temperature swings can be stressful on the fish, corals and any other invertebrates in the tank.

There are other downsides to running a "Hot" tank. As the aquarium water heats up it can hold less and less dissolved oxygen. So, running your tank in these upper extremes can prove fatal for your livestock if you don't have a protein skimmer (excellent at oxygenating the water) or surface agitation from power heads or return flows from sumps breaking the water surface. If you've just set up your tank and it's winter time and you notice your tank temperature creeping up, just imagine what it's going to be like in the spring or summer when the house temperature could be a few degrees warmer. Yikes!

Do I really need a chiller?

The first thing you should do before spending your hard earned cash on an expensive water chiller is to run a fan or two over the top of the tank or sump. Fans can do a nice job of lowering the temp a couple of degrees. The downside is the increased levels of evaporation which means doing water top offs more frequently. This can be a pain in the you know what, and it can be expensive if you factor in the cost of the Reverse Osmosis and Deionization filters along with the cost of running the fans. Aquarium chillers can use lots of electricity too though, especially if they are undersized for the aquarium the are trying to cool down.

If you're keeping a FOWLR (Fish Only With Live Rock) saltwater aquarium setup you probably won't be running metal halides or the very high output fluorescents. Why waste the electricity on animals that may only marginally benefit from the higher output lights, if at all? So, you most likely won't need a chiller. Try a fan to bring down the temperature a degree or two.

A reef tank setup or aquarists keeping coldwater species may need to invest in one of these units if their aquarium temperatures are getting too high. Or, if running the fan works, but the frequent water top offs (usually daily) are getting old, you may want to invest in a chiller.

Aquarium water chiller options

Chillers are usually rated based on horsepower and BTU (British Thermal Units). BTU's are the measurement units used to describe the amount of energy required to change one pound of water one degree Fahrenheit. Manufacturer's will usually recommend the maxiumum aquarium size that the aquarium chiller can be used on. Use that as your guide. If your tank is on the borderline size wise and you're having a hard time deciding between two similar units, go with the higher capacity unit. It should save you in energy costs.

Below is a table of sample chiller sizes. This is just for example purposes. Of course, sizes and capacities may vary depending on the unit. This is just to give you a general idea of what's available.

Size Max Aquarium Size Temperature Range Price Range (USD)
1/3 360 gallons
(1363 liters)
60 - 85 °F
(16 - 30 °C)

1/4 260 gallons
(984 liters)
60 - 85 °F
(16 - 30 °C)

1/5 180 gallons
(680 liters)
60 - 85 °F
(16 - 30 °C)

1/10 70 gallons
(265 liters)
60 - 80 °F
(16 - 27 °C)

1/15 50 gallons
(190 liters)
60 - 80 °F
(16 - 27 °C)

1/20 25 gallons
(95 liters)
60 - 80 °F
(16 - 27 °C)

You will usually see two different styles of chillers as well. There are "drop-in" and "inline" chillers. The drop-ins have a cooling coil that is placed in the sump. The upside to these drop-in units is the fact that you don't have to run any plumbing and you don't need a separate pump to get the aquarium water to the chiller and back. They are not in favor as much nowadays though.

The inline units are more frequently available. You will most likely need an aquarium pump and some flexible tubing to run back and forth from the tank or sump to the chiller. It stinks to get the chiller delivered and then have to wait until the next morning or the weekend to go out and purchase a pump! So, keep that in mind.


These are pricey pieces of aquarium equipment. Do your homework and don't get burned on a crappy unit. Hobbyists on forums will gladly share their experiences with you. Go to your favorite search engine and type in the name of the chiller along with the word "Review" and see what comes back. There may be published reviews for you to read. Just be warned though that sometimes these published reviews may be a little sketchy. Perhaps the merchant is trying to make sales or the manufacturer is doing some "marketing". Be careful and pay attention to what your are reading and you'll be sure to pick out an aquarium chiller you'll like.

Some things to keep in mind when shopping for a chiller:

The main thing an aquarium chiller can do for you and your tank is to keep those temps stable. A stable temperature is one component that can help lead to healthy fish and corals. If you are one of those crazy marine fish breeders (wink) perhaps you could use a chiller to perform manual temperature swings to help trigger spawning events. Also, don't forget to help your fellow hobbyists. Let them know if you have a good one. Give them the pros and cons and help them make a better decision when they go to buy a chiller.

Thanks for reading.


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Go here: Aquarium Chiller Forum