Tips For Keeping Your Aquarium Cool in Hot Weather

Whether you have a freshwater or saltwater aquarium, rising temperatures in the summer time can be a cause of concern. Aquariums shouldn’t be allowed to get hotter than 83°F, or dissolved oxygen levels in the water will start to diminish. This triggers a competition between fish and invertebrates for oxygen  leading to a very stressful situation, and possibly even death, for your aquarium inhabitants. Detailed below are some tips to help keep your aquarium cool when temperatures rise.

Evaporation and Air Circulation

Evaporation, when water turns from liquid to gas, helps to cool aquarium water. Evaporation occurs with the addition of energy to the water, such as heat transferred from lighting, pumps, and the room’s air temperature amongst other things.  In order for evaporation to occur, the water surface must have exposure to the open air. Plastic hoods and glass canopies hinder the amount of evaporation by limiting air flow and trapping the moisture and heat in the aquarium. Opening the hood or canopy, or removing it all together can help when you’re battling high temperatures. You can also increase air flow and evaporation with a small fan. Fans should be pointed to blow across the surface of the water, and can be a big help in drawing heat away from an intense lighting fixture. How many fans you need depends on the size of the tank, but even one small fan can make a huge difference. Cutting back on how long the lights stay on can also help by reducing the amount of heat energy put into the water.

Water Circulation

Good water circulation is key to keeping the water cool. Heat energy dissipates at the water’s surface. Furthermore, gases exchange at the surface of the water; Carbon Dioxide leaves the water, and Oxygen is introduced. Without good circulation the water’s dissolved oxygen levels can become alarmingly low at higher tank temperatures.

So what’s considered good circulation? Circulation can vary from tank to tank depending on how the tank is decorated, the type of inhabitants you have, tank dimensions and more. Generally speaking, fish only tanks should have enough water flow to turn the water over about 10-40 times per hour (tph). Tanks with soft corals should be turned over about 10-30 tph. Mixed reefs (soft and hard corals) and tanks dominated by large polyp stony corals should be turned over 30-50 tph. Small polyp stony coral aquariums should be turned over at least 40-80 tph. These are simply rules of thumb and may not apply to every tank, but by having adequate water flow, the tank should naturally run cooler.

Break out the Ice

When worse comes to worse, ice can be a simple solution. Freeze water in clean bottles that have never been exposed to soap or other detergents. Don’t use ice packs as they can leak, and don’t throw ice cubes directly into the water either. Unless you’re using un-chlorinated water, you will be directly adding chlorine and/or chloramine to your tank water. Bottles are easier to take out when the temperature hits the right level. Let the frozen bottles float in the tank or in the sump. Be sure to monitor the temperature–there’s no easy way to control how much or how quickly the temperature in the tank will drop. While reducing the temperature can be imperative, it must not be done too quickly.

Employ a Chiller

If maintaining temperature is a big issue for you, it may be best (or necessary) to invest in a chiller. Chillers come in a variety of sizes and styles that can be plumbed in-line or placed in the sump. To buy the right size chiller for your set-up, you’ll need to know the size of the aquarium, and how many degrees you want to drop the temperature of the tank.

Understanding of how chillers are rated will also help you to judge which chiller to purchase. The easiest rating to find on a chiller’s packaging is the horsepower. Unfortunately, the amount of horsepower doesn’t directly equate to how much heat the unit will be able handle. The HP rating can be useful as a general guide or for determining how many watts the unit is going to use, but the better number to look for is the BTU (British Thermal Units) rating. Chillers are rated in BTU’s, just like air conditioners. More accurately, they are rated in BTU’s per hour (BTU/hr). A BTU essentially equals the amount of energy it would take to raise the temperature of a pound of water 1ºF. Chillers remove BTU’s (heat) from the water, so BTU/hr gives you a perspective of how much heat removal the unit will achieve within a time frame. While HP lets you know how much work the chiller will do, the BTU rating shows you how efficient the unit is. The higher the BTU rating, the cooler your tank will be.

There are many factors that will influence how the chiller performs including flow rate, tank size, and heat sources (lights, equipment, ambient room temperature). All of these things have to be taken into account when sizing the chiller up. Just because your friend’s ¼ horsepower chiller cooled his 75 gallon tank to his satisfaction, doesn’t mean it will be an efficient unit for your 150 gallon tank– regardless of what the manufacturer says on the box. As a very general rule, a 1HP chiller should be able to remove about 12,000 BTU’s at peak efficiency. From there, we can assume a ¼ HP chiller should be able to remove a quarter of 12,000, or 3,000 BTU; a 1/2HP chiller should do 6,000 BTU, and so on. Some models achieve better numbers than this, and some less. Ask a salesperson if you’re shopping for a chiller, we can tell you more about the options and help you buy the right chiller for your system.

Below is a guide as to what horsepower chiller you can use to drop the temperature about 10°F. Remember that different manufacturers have different BTU ratings for their chillers, and as such a chiller of one brand may outperform a chiller of another, regardless of their horsepower. It may be necessary to go to the next size up for larger jobs requiring more than a 10ºF drop in temperature. At the very least it’ll be more energy efficient to do so, as the chiller will have to turn on less frequently than it lower HP models. Be sure to check the packaging to see what flow ratings each manufacturer recommends as well.

Chiller Size(in horse power)	Tank Size (in Gallons)
1/15 HP	30
1/10 HP	60
1/6 HP	80
1/5 HP	100
1/4 HP	130
1/3 HP	180
1/2 HP	250
1 HP	500

There are several inexpensive ways to lower the temperature in your aquarium, before having to resort to an expensive chiller. Employing multiple strategies can work wonders, but if you decide to buy a chiller be sure you choose best fit for you situation. The most important tip of all however, is to be ready. You don’t dead fish, inverts or corals to be the indicator that there is a problem with high temperatures in your tank. Monitor your tank as the outside temperatures rise so you can be prepared before there is a real problem. Hopefully, this brief outline helps you keep your tank cool this summer!

Thanks,

Jeff Berdel

Ice Cubes image referenced from wikipedia and originally posted by Darren Hester