Cooling Fans

Cooling fans help prevent your aquarium from overheating and are especially important if you do not have an aquarium chiller. The heat generated by multiple powerheads, skimmers, return pumps and aquarium lighting can easily cause temperatures in saltwater aquariums to rise to levels that are deadly to fish and corals.

aquarium cooling fan

Aquarium Cooling Fan

It should be noted, however, that cooling fans are nowhere near as efficient as aquarium chillers, but they will help to lower tank temperatures by that critical 1 or 2 degrees. An aquarium chiller is still a necessity if you are planning on keeping delicate corals.

Temperature Upper-Limit For Reef Aquariums

As discussed on our page on Ideal Water Parameters For A Reef Aquarium, the maximum temperature that can be tolerated most fish and extremely hardy corals is 29 degrees C (84 degrees F).  Fish are cold-blooded and their body temperature and metabolism is directly related to the temperature of the water they are living in.  Anything more than 29 degrees C for an extended period of time is actually cruel!

The 29 degree C upper-limit also applies for corals that are considered extremely hardy — leathers (typically Sarcophyton, Sinularia and Lobophyton) and sea mats (Zoanthids and Palythoa) are usually tolerant of higher temperatures.

Small-polyped stony (SPS) corals require that temperatures stay within the optimal range of 24 to 27 degrees C (75 to 81 degrees F), if any sort of longevity is to be expected.  From my experience, the upper-limit for most large-polyped stony (LPS) corals is 28 degrees C (82.4 degrees F).

How Do Cooling Fans Help To Lower Water Temperature?

Cooling fans lower water temperature by promoting evaporation. Much like how you would blow over a cup of hot coffee to cool it, fans are directed to blow across the surface of the water to lower the temperature in a tank.

A major downside of using cooling fans is that evaporation increases greatly, requiring that fresh RO/DI water be replenished every other day. Or, in the case of nano tanks, every day!

Cooling Fans For A Beginner’s Saltwater Aquarium

Most beginning hobbyists balk at the idea of getting a chiller from the outset.  Unsure if they will stay in the hobby for long, a chiller is a hefty investment indeed.  At the advice of their local fish store, most will go with one or two cooling fans.

Some misinformed fish store staff may even tell the beginner that the increased evaporation means that the water is being cleaned each time the tank is topped off with fresh water. If only I had a dollar for every time I’ve heard this story!

Evaporation does not remove pollution, impurities or nutrients from the water.   Pollutants are left in solution since what evaporates is pure water. Top-off water should strictly be fresh water (RO/DI or distilled) and not saltwater!

Installing Cooling Fans Over An Aquarium

Cooling fans should be installed securely with clamps, ensuring that there is no possibility of one falling in and electrocuting the livestock.

aquarium cooling fan over nano tank

Cooling Fan On A Nano Tank

When clamping a cooling fan directly to the glass of the aquarium, ensure that there is a small sheet of rubber between the jaws of the clamp and the glass. Most manufacturers will provide for this as it makes the grip of the clamp much firmer, reducing the risk of the clamp slipping and the fan falling into the water.  Once in place, it is a good idea to check the clamp once in a while as vibration can sometimes cause the clamp to loosen.

Types Of Cooling Fans Suitable For A Saltwater Aquarium

You will need at least a 4-inch diameter fan with sealed bearings. The fan should be one intended for aquarium use. Tiny computer fans or domestic-use fans will usually fail in a matter of months due to the high humidity and salt creep.

Bear in mind also that the cooling fan you choose will need to be left on 24/7 unless temperatures in your area drop to levels that are sufficient to cool your tank at night.

Cooling Fans, Evaporation..  And Rust Everywhere!

The rapid evaporation brought on by cooling fans increases the overall humidity of the room that the aquarium is in.  The effect of this increased humidity is that metal objects in the same room as the aquarium will start to rust.

I’ve even had stainless steel dinner forks left in a placement holder on the dining table about ten feet away from my tank develop rust spots!

This is an important point that most authors leave out for some reason when discussing  aquarium cooling fans.

Cooling Aquarium Lights

Metal halide lighting generates an enormous amount of heat.  Having one or more cooling fans directed upward at a metal halide pendant or T5 light fixture blows heat from the bulbs away from the surface of the water, easing the burden on the chiller. Cooling fans used in this way may even extend the life of the aquarium lights and ballast.

Used with a timer, the fans can be turned on or off automatically to coincide with the lighting schedule.

Cooling Fans Or Chiller?  The ‘Wait And See’ Approach..

I can honestly tell you that I could have kept many of my early corals alive had I invested in a chiller from the very start.

In the tropics where I live, ambient room temperatures sometimes rise to 28 degrees C during the day. Which means that running a reef tank with all equipment on can easily bring the water temperature up to around 30 to 31 degrees C (86 to 87.8 degrees F) without a chiller or cooling fans!

I installed two cooling fans, one over the main display and one over the sump tank. Evaporation was tremendous, but it brought the daytime/lights-on temperature down to around 29 or 29.5 degrees C.  Corals survived, some even thrived, but not for more than several months.

So instead of adopting a ‘wait and see’ attitude of using cooling fans and hoping for the best for your delicate corals, do invest in an aquarium chiller. As responsible aquarists, it is our duty to provide the most comfortable living environment for our aquarium inhabitants.

Links to more Saltwater Aquarium Setup pages:

Aquarium Tank Size | Length, Width And Height

Ideal Location For Your Saltwater Aquarium In Your Home

Ready-Made Aquariums

Drilled Overflows Vs. Siphon Overflows

Aquarium Stands

Why Beginning Hobbyists Should Avoid Starting A Nano Aquarium

How To Setup A Nano Tank

Aquarium Chillers

Aquarium Sump



Aquarium Covers | Put A Lid On It!


What You Don’t Need For Your Saltwater Aquarium!


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