How to Keep Your Aquarium Cool
(or . . . Do I need a chiller?)
by Aquariumpros.com staff
Reprinted with permission
For those of you (lucky people) that live in warmer climates, keeping
your aquariums cool during the summer months is a challenge. The Aquarium Professionals
Group receives dozens of calls each summer from concerned hobbyists seeking advice on how
they can lower the temperature in their aquariums. Out here in the Chicago area, we've had
reports of tanks running from the mid 80s to the mid to high 90s (Fahrenheit). In many of
these cases, the aquarium owners do not have air conditioning in the room where the
aquarium is kept, or they have no air conditioning at all. Out here, outdoor temperatures
usually only get into the 90s from late June through August. Keeping the aquarium room
cool is a first step, especially for marine aquaria. The cost of running an air
conditioner for a few months is a small price to pay to keep our finned friends alive.
There are some instances however where air conditioning isn't possible,
and what if air conditioning alone isn't doing the trick? The obvious solution is to add
an aquarium chiller, but this is an expensive option. Even at internet and mail order
prices, chillers can cost between $500.00 and $1800.00, depending on model and the
horsepower needed. In some cases, a chiller is the only option, regardless of cost. This
will depend on the type of aquarium you keep and the temperature drop needed to cool the
tank. We'll talk about chillers a little more later, but first let's look at some other
methods for cooling an aquarium during the summer:
How high temperatures hurt aquatic life. With fish, it's not always
the high temperature that kills. Many fish die in tanks running too hot due to low
dissolved oxygen (DO) levels in the water. The warmer the water, the less dissolved oxygen
(DO) it will hold. This is also true for water with a higher density. A given volume of
saltwater contains far less DO than the same volume of freshwater, so freshwater aquarium
fish tend to tolerate higher temperatures because there is more oxygen available to them.
Other factors that influence whether fish will be affected by high
water temperatures are the number (bio-load) and species of fish kept in the tank. The
higher the bio-load in an aquarium, the greater the risk that oxygen will become depleted
when the water gets warmer. If you have a fish-only tank (fresh or saltwater) and don't
have air conditioning, keep your aquarium under-stocked! The species of fish are also an
important factor. Freshwater Discus (Symphysodon sp.) thrive under high
temperature conditions. Fish that inhabit warmer water in nature will obviously do well
under those conditions in the aquarium (another good argument for designing the
environment around the desired livestock when setting up a new aquarium). Keep in mind
that we're only discussing fish right now. We'll get to live corals and other
The ideal temperature for most fish-only aquaria is between 76 degrees
and 82 degrees Fahrenheit. If you only have fish, the aquarium is stocked properly, and
you only need about a 2 to 6 degree temperature drop, here's a few things you can try:
- Buy an air conditioner! Sometimes this is the only solution.
- Aerate with a strong air pump! This will help to increase the exchange of gases at
the waters surface, thereby helping to raise DO levels. It will also aid heat exchange at
- If your aquarium is well-covered, open the covers on your tank, and place nylon
netting over the openings to prevent fish from jumping out. This allows heat to escape.
You can aid this process further by directing the air-flow of a small fan across the top
of the tank.
- If your aquarium equipment is in a closed cabinet stand below your fish tank, open
the cabinet doors and place a fan circulating air into the cabinet area to allow heat
created from pumps to escape.
- Purchase a small canister filter designed with the motor on top (see our line of
Eheim canister filters for example) and immerse the lower half of the canister in a bucket
of ice to create a (relatively) inexpensive quick-fix chiller. Replace the ice as needed
but please be careful! This method is tricky and requires some experimentation to prevent
the tank temperature from fluctuating too rapidly (a major source of stress leading to
fish diseases). Monitor the temperature of your aquarium carefully until you get the ice
replacement times down to a science to maintain a stable temperature.
- Close the shades on windows in the room. Even indirect sunlight will raise the room
temperature by a degree or two and every little bit helps. You can also reduce the amount
of time the aquarium lights are on. The tank lights contribute greatly to higher water
temperatures. Don't leave the lights off all the time though. That's bad for your fish
too! If you have a freshwater planted aquarium, which requires at least 8 hours of light
per day, you may have no choice but to buy an air conditioner or a chiller to solve your
- DO NOT unplug your aquarium heater! This is a common mistake that often backfires. An
aquarium heater that's working properly will shut off when the aquarium is at the proper
temperature. Unplugging the heater could cause the temperature to drop too far at night in
situations when it's hot during the day but cool at night and the windows in the aquarium
room are kept open.
When a Chiller Becomes a Must-Have
Live reef aquariums and invertebrates:
Sorry folks, but if you can't use air conditioning and you own a marine live-coral reef
aquarium, a chiller is your only option if the temperature of the tank is more than 84
degrees Fahrenheit. If you can have air conditioning but don't, get some! You don't have
an option there either. Trust us when we say that replacing invertebrates that die in a
hot reef tank is not only morally wrong and unethical, the cost of doing so will far
exceed the cost of an air conditioner (and/or a chiller). If you are running air
conditioning and your aquarium is still over eighty degrees, you need a chiller.
When it comes to keeping aquatic animals, our position is clear:
If you can afford to buy a nice aquarium, you should first make sure you can also afford
to equip and maintain it correctly. In our opinion, a good aquarium chiller should be part
of any live reef aquarium purchase, unless the aquarium will be kept in a room that
remains very cool year round. This is also true for any specialized aquarium with lighting
and pumps that create high aquarium temperatures.
If you do need to purchase a chiller, you may want to take note of
these important tips. Remember that a chiller will emit quite a bit of heat. Do not
enclose the chiller or place it inside a cabinet stand, unless the cabinet stand has been
designed to house a chiller (a one foot square opening that matches the exhaust opening on
the side of the chiller, and a one foot, fan-assisted opening at the other end of the
cabinet for fresh air). Do yourself a favor. SAVE THE PACKAGING THAT CAME WITH YOUR
CHILLER! You'll need it for at least thirty days from the date you bought the unit. Before
you buy a chiller from a mail-order or discount internet source, make sure you know the
return and service policies of the company with which you're doing business. Chillers can
be easily damaged in shipping, and often that damage will not be immediately apparent.
Chillers are heavy pieces of equipment and are expensive to ship. We've seen chillers that
worked great for the first two weeks and then went kaput due to hidden damage to a relay
or the compressor. It's worth spending more money to buy your chiller from a source that
will help you if you have problems.