Knowledgebase > Keeping Your Aquarium Cool (Updated: 5/18/2012) by Keith MacNeil, a Reef Squad Member
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Q10261 - HOWTO: Keeping Your Aquarium Cool (Updated: 5/18/2012) by Keith MacNeil, a Reef Squad Member
Our aquarium inhabitants rely on us for almost everything. Stable conditions including the water temperature within the tank are very important to a successful tank. With summer fast approaching we need to start watching for rising temperatures within our tanks and starting thinking about how we are going to deal with them. There are many causes for warm water temperatures as well as many solutions to help keep them at acceptable levels. In this article we will touch on some of the causes of excess heating of the tanks water as well as some ways to help negate them.



Reef tanks and marine tanks alike both need good water movement and circulation for the inhabitants to be healthy. To provide this water movement in the aquarium pumps and/or powerheads are used. Both internal (submerged) and external pumps can add heat to the water as a means of cooling themselves. Different pumps will add different amounts of heat to the water. With a little research, you will be able to find out which pumps transfer the least amount of heat and the ones that transfer the most amount of heat to the water and can choose a pump that works best for your system.


Corals in a reef tank require high intensity lighting to survive. These high intensity lighting fixtures can become another major heat producer. It will not matter whether you are using VHO, T5, PC or metal halide lighting. All these lights will produce heat that can affect the water temperature in your tank especially when enclosed within a canopy. LED lighting may be one of the only exceptions and can be a great alternative especially for nano tanks where cooling can be more difficult.

Room temperature

Room temperature will also have a large affect on the temperature of the aquarium. The higher the room temperature is, the higher the temperature of the water in the tank will be. Summer time is usually the worse time of the year when dealing with room temperature problems, but even spring and fall can have their share of extremely warm temperatures. If lucky enough to have central AC, this may not be an issue for your tank, but otherwise trying to put your tank in a room that generally stays cooler (i.e. doesn’t have the sun shinning in the room all day long) can go a long way in keeping the temperature lower.


Lucky for us hobbyists there are many options for helping to keep a stable environment (i.e. temperature) within our tanks. Some methods are very simple, while others are a little more complex. Depending on the size of the tank and the amount of temperature changed needed, you will need to choose what method will work best for your application.


The use of fans can be a fairly inexpensive method for cooling your tank. There are a couple of different applications that can be implemented alone or together. First is using fans to blow the hot air that is produced by lighting fixtures away from the tank. Although this can lead to increased room temperatures, it will at a minimum keep a major heat build up from occurring directly over the tank. There are many choices in fans as well that can either be mounted directly to the rim of the tank or attached to a canopy.

The second use of fans for cooling the aquarium is by blowing air across the water surface. By blowing air across the water surface it will cause an increase in evaporation in the tank. In turn the evaporation will help cool the water in the tank. This is called evaporative cooling. Depending on the room temperature and humidity, a fan can cool a tank by 2-4 degrees fairly quickly. If the room temperature is high and humidity levels are also high, this will dramatically affect the ability of evaporation to cool the tank. One obvious disadvantage to this cooling method is the amount of water that will need to be replaced on a daily basis. For larger tanks, this can easily amount to 3-5 gallons per day from evaporation (using an auto-top off system comes in handy for this). Some fans can also be loud, adding to the noise levels coming from the aquarium.

Cooling Fans

Chillers in my opinion are by far the best method of cooling an aquarium. Chillers are basically heat exchangers. Most chillers use titanium coils and a refrigerant to cool the water as it passes by the coils. There are two main types of chillers available on the market today, inline and drop-in. The inline chillers require water to be pumped through the unit. The cooling of the water will occur within the coils located inside the chiller. These chillers can be placed anywhere in relation to the tank. For example the chiller can be placed outdoors (in a protected shelter), in a garage or in a different room as long as the user is able to pump water into the unit. The drop-in chillers have the titanium coils external to the actual unit. The coils need to be placed into the sump where water can pass by the coils to be cooled. The advantage to this type of a chiller is there is no plumbing needed, so it is very simple to install. One of the disadvantages of the unit is it needs to be placed right next to the sump as the coils and flexible refrigeration line coming from the chiller are normally around 3-5 feet long.

Whether the inline or drop-in chiller works best for you and your tank, it is important to allow plenty of ventilation around either unit. The chillers will give off heat while they are cooling the water. If the chiller is placed in a closed area, such as a closet or aquarium stand with out any opening, the unit will not be able to chill properly and could add extra heat to the tank.

Controllers to help keep temperatures stable

Chillers will require a temperature controller to function. Some units come with built in temperature controllers while others have external or remote controllers.

What are temperature controllers and what can they do for your tank? As mentioned, chillers require a controller to function properly. A temperature controller will turn on and off a chiller or other equipment such as a fan at a given temperature setting.
In-Line Chillers
Drop-In Chillers
For example if you want your tank to get to a maximum temperature of 80 degrees F, you would set the controller to turn on the chiller when the temperature hits 80 degrees. The controller will turn on the chiller when the temperature gets above 80 degrees and then once the water has been cooled below 80 degrees it will automatically turn the chiller off.

There are two basic types of controllers available, a single stage and a dual stage. A single stage controller will turn on and off one piece of equipment, such as a chiller or a heater. A dual stage controller will turn on and off two pieces of equipment, such as a chiller and heater. For the most stable temperature control of your aquarium, the dual stage controllers are the best option. The dual stage controller will turn on the chiller when the tank gets too warm and will turn on your heater when the temperatures get too cold. You can even get controllers such as the Digital Aquatics Reef Keepers or Neptune Systems Controller to monitor and control other aspects of your tank such as pH and ORP as well as control your lighting system and are well worth the money.

Floating Ice Method

The floating ice method can be done many different ways, but one of the easiest methods is using empty two liter soda bottles (or smaller bottles for smaller aquariums). Fill the empty bottles with water and put them in the freezer, making sure there is enough room in the bottle for expansion of the water when it freezes (leave the top slightly open to allow air to escape during the expansion of water to ice). Then once the bottles are frozen, they can be placed in the sump or main tank to help chill the water. One of the advantages of this method is that it is very inexpensive to do. But there are many disadvantages to this method including you will need to change out the bottle through out the day to help maintain a stable temperature in the tank. Unless you are home 24/7 this may be impossible to accomplish. This is a very “hands on" method of tank cooling but not the most efficient cooling method. People have also used RO/DI ice cubes (or other filtered water cubes) to help with cooling their tanks. If you use ice cubes, just make sure your salinity doesn’t drop too much from them.


Many nano tanks come with fully enclosed hoods that contain their lighting system. Even when supplied with a fan built in to remove some of the heat, the canopy can trap heat within the aquarium. With their smaller volume of water, they are also more subject to quicker changes in water temperatures than a larger tank. The above list of options can work on nano aquariums, but many times a chiller can be your best option.

InIn years past chillers have been very bulky and their horsepower (HP) was too large for smaller nano tanks. Luckily many chiller manufactures have seen how popular these tanks have become and have made some lower HP chillers available for nano tanks. JBJ offers a 1/15 and 1/10 HP chiller. Other manufactures like AquaEuroUSA, Coralife and Sunlight Supply also offer chillers for tanks under 50-60 gallons.

All of the chillers will sit next to or below the tank and have water pumped through them by a small powerhead like a Maxi-Jet or Mag-Drive pump. You will also need some vinyl tubing to hook the powerhead up to the chiller as well as running the water back up to the tank. JBJ makes a Connection Kit that can make life a little easier as well. I would also like to note that the chiller should not be placed inside of a fully enclosed stand as the chillers need to pull air through them to cool the water.

One last chilling option I would like to mention for the nano tanks are the IceProbe and Microchillers that are available. These units are good for around a 10 gallon tank to lower the temperature around 6ºF to 8ºF below ambient air temperature. These are a good option either for acrylic tanks that can be drilled (for the IceProbe) or for tanks where a hang on the back type filter (the Microchiller) can be used. One of the advantages of these units is they don’t use any refrigerant so they tend to be more reliable and environmentally friendly. To read more about how these chillers work you can read here.



There are many factors that can be very difficult to control in a reef tank, temperature does not have to be one of them. While you do not have to keep your temperature at a single reading, the stability of keeping the temperature within a few degrees swing will help the overall health and well being of your tank. With the temperature staying within a controlled range, you are able to eliminate one factor that can put stress on your tanks inhabitants and hopefully lessen other stressors that can affect your tank.
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Approved Comments...
Article is well written, and well explained so that I can understand it. Approved: 5/28/2010
Great article and very useful actually. I was waiting for this. We had 90 F in MA past few days and temp in my tank sky rocketed to 82.6 one day I almost had a heart attack. Can any of you recommend a good chiller for 65 gal Red Sea Max 250? EDITOR'S NOTE: Send us an email at and we can make some recommendations Approved: 5/28/2010
Nice overview! Approved: 5/28/2010
I also live in New Haven, CT and during the first week in April, the outside temp was a good 20 degrees warmer than normal. My tank water hit 86 for a short while & we brought it down to normal temp using Zip-Lock baggies filled with ice cubes. Fortunately nothing perished but the high temp brought about a algae bloom that took weeks of syphoning and water changes to get rid of. My prized Wessophyllia brain coran had its fire engine red color change to pink and the bright green is now somewhat drab. So be sure and have a chiller on your tank, go and get one now. Im extremely fortunate that no corals died and your tank may not be as lucky as mine was. Approved: 5/27/2010
I have a AC next to my 55g/l I make a small hole in my canopy installed a flex pipe from my old sump and this keeps my tank cold Marco Castillo Approved: 5/9/2009
Im first time Aquarist (?) and been worried about up-coming warm weather. this article gave me great ideas on how to cope. My fish dont seem to like the light on anyway, only use it for plants ~ 8 hrs/day the light "on" time will be cut back first. It would have been nice to be able to print article without photos. Forget previous printing comment - found magic print click. Approved: 5/9/2009
Covered most of the popular methods of cooling a tank. Nice to see you are not just focusing on one type of brand or method! Approved: 5/9/2009
Great information not complicated for non experts like me, I have a 75 gallon marine aquarium what cooling that bis energy saving and economical that I can purchase Approved: 5/9/2009
Its always great to learn new, eco-friendly ways to manage your aquatic environment. Approved: 5/8/2009
this article gave specific details on cooling. Very informative and also listing many different options available with advantages and disadvantages on each one. Approved: 5/21/2008
It shows cooling options that I did not know about. What about the physiology of the fish? I know that they are isothermic. How can you minimize the stress on them if your chiller fails and the temperature goes high? What about a power outage in a cold climate? Approved: 8/7/2006
Window AC is the way to go for room temp problems. Why spend $$ on a chiller that benefits only the tank, when for [less] $$ you and the tank stay cool. Im surprised the article didnt suggest window AC as a solution. Approved: 8/2/2006
Simple and comprehensive information. Approved: 8/2/2006
do you guys have any more suggestions on keeping your tanks cool? Approved: 8/1/2006
honesty Approved: 8/1/2006
I have a chiller, but it has blown 2 times and this is a helpful solution until you can replace or fix the chiller Approved: 7/31/2006
Its on the money. Approved: 7/29/2006
The commentsof your article are very useful to everybody, specialy for the beginners in reef aquariums, where the temperature is very important in the maintenance of corals. Approved: 7/29/2006
Honest&Truthful,Factual to the point artical. Approved: 7/29/2006
Good summary article although you didnt mention the costs of chilling equipment which can be quite high (hundreds of dollars). Ive got a 90 gallon tank and have combined an internal fan over the sump for evaporative cooling with use of frozen RO water (to replace that lost from the fan) that is placed in the tank daily. The water temperature fluctuates about 2-3 degrees (77-80 F) and seems to be fine for the reef items I have. Approved: 7/28/2006
Basic itroduction/reminder on chilling the water in tank. Gives a good direction on what and how to do. Approved: 7/28/2006
I would have appreciated greater detail as to the distance of the lights from the water surface, glass barriers between the water and glass, size of fans, direction of fans blowing, differences between heat transfer in acrylic and glass aquariums, etc. Approved: 7/28/2006
As always an inportant subject and some very good solutions. I personally look forward to the articles and print out each and every one for future referance and I have had a salt tank set-up for over 12 years and some of my fish are that old also. Thanks for great info Jeff Bradway Brimfield, Massachusetts Approved: 7/28/2006
the article was easy to read as it presented complicated information in an easy to understand way and went into detail that too was easy to understand Approved: 7/28/2006
you can give the options-you should be more forceful Approved: 7/28/2006
We had a "heat wave" (90 degrees hardly constitutes a heat wave in some parts of the country)in Seattle this past weekend and my tank temperature remained at 80 degrees for 3 days, lukily there are no fish in right now (cycling). We do not have AC, so the temp of the house was very hard to control, thus the tank just succombed to the heat. However, fish will be living in there in the next month so this article helped me to understand and be prepared for our future hot summer days! Thanks, Becky Approved: 7/28/2006
Very practical. Approved: 7/28/2006
very useful informations for temp contntrol in the reef tank, thanks so much for the info. sam. Approved: 7/28/2006
We just had a nasty heat wave in So Cal my chiller died n the middle of it my water got to 95 Approved: 7/28/2006
The article gave many choices for every budget. Thanks Approved: 7/28/2006
You did not mention the use of a window air conditioner unit in the room with the thank. Adding one for $159 decreased my 120 gallon reef tank temperature from 86.3 to 79.3 in 4 days. In the 3 week it has been running the tank temperature has stayed constant within 2 degrees, not to mention that the room is way more comfortable. I live in Georgia and its July and VERY HOT! This method for me was more efficient than lowering my central air unit way down and cooling rooms we were not using right then. My den was an add-on room and thus the cooling and heating vents are farthest away from the main unit and the room would stay very warm even with ceiling fans. Approved: 7/28/2006
First time Ive seen mention of my method (cooling by evaporation) with a fan blowing across the water surface. With up to seven power heads running at one time, two 4 atinic blue tubes, and a 400W metal halide bulb, Im still able to keep my tank at a fairly constant temperature of 75 Degrees. Approved: 7/28/2006
Just basic information that is widely available. Approved: 7/28/2006
With the heat wave that is going on in California I am having tank temperature problems. This article gave me some ideas what to do in extreme case. Approved: 7/27/2006
Article Details
Created on 7/25/2006.
Last Modified on 5/15/2012.
Last Modified by Dot Yuson.
Article has been viewed 27958 times.
Rated 9 out of 10 based on 151 votes.
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