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.

Causes of Heat in the Aquarium


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.

Cooling Options

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.


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.

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.

Chilling a nano tank

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.

In 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.

How to setup an aquarium chiller


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.