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Tips For Keeping Your Aquarium Cool in Hot Weather

Ice CubesWhether 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

Circulation pumpGood 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!
    Jeff Berdel

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


  1. avatar

    I’ve been thinking about getting an aquarium and getting some interesting fish, but wanted to get some good tips first. You wrote that temperature is key, and if the temperature gets too high you should have ice on hand. I’ll have to remember this, as I would love to keep the fish alive and happy for as long as possible. Thanks for the blog.

  2. avatar

    Hi Rachel, Ice should be used in an emergency only and in a bag, water bottle or other container. Never drop ice cubes directly into your tank since it can be very dangerous if the fish or any other animals eat it. Feel free to let us know if you have any questions while setting up your new tank.

  3. avatar

    My friend suggested me to put ice cubes in fish tank..I used to put it daily in aquarium.My 3 fishes died.Is it a reason of their death?

  4. avatar

    Hello Natasha, I wouldn’t be able to say if it killed your fish without a lot more information about the tank but putting ice in a tank is dangerous. If a fish eats anything frozen, whether its an ice cube or unthawed frozen food, it can cause internal damage in their gut. If a tank is too warm to the point that you need to put ice dubes in it every day, it may be time to invest in a chiller for the system.

  5. avatar

    I had no idea that hot weather could heat up an aquarium to the point where it could harm the fish. I have always loved anything to do with the ocean, so I feel like a salt water aquarium would be a perfect touch for our apartment. I definitely think that I should look into water circulation techniques that could help to make sure that it stays cool during the summer.

  6. avatar

    My wife just bought me a used 75 gallon tank which I’ve cleaned from top to bottom ( its my 3rd tank over 50 gallons) and its been running fine, it has a marine land magnum 350 filter and a Inline heater but the heat won’t drop below °84 and I even unplugged the heater. I can’t afford a chiller because all our money is used for my pancreatic cancer.

  7. avatar

    Hello Pat, Try the other suggestions in this article like running a fan across the surface and increasing water circulation.

  8. avatar

    I’m worried because I have 3 comet goldfish In a 10 gallon tank and they just sit at the bottom and don’t swim a lot, and the tank always gets really hot

  9. avatar

    Hello Hannah, Have you tested the water quality in the aquarium (Ammonia, Nitrite, Nitrate, pH)? How high is the temperature getting? What type of filter is on the tank? A 10-gallon tank is far too small for Comet Goldfish and the high temperature as well as any water quality issues will certainly affect their health. For more information on keeping Comets, you can view our other blog articles like How To Care For Carnival Fish or you can contact our Fish Room staff at 717-299-5691, option 6.

  10. avatar

    We are wanting to use Betta fish for an outdoor reception. It would be from 5-10 so not in the heat of the day. It would be in mid May. Would they survive?

  11. avatar

    Hello Anonymous, That would be difficult to say, especially without knowing where you are and what the weather is going to be like in mid-May. Bettas should have a consistent temperature around 76-80 degrees F. If the water (not air) temperature can be safely and consistently maintained within that range during the event, they would probably be fine but keep in mind that direct sunlight, cool breezes and small containers can allow the temperatures to change easily.

  12. avatar

    Hi Eileen.. the article says not to throw ice or frozen water directly because of chlorine and I saw your replies as well.. But will it be alright if I collect tank water in a bottle and keep it frozen (but not turn it into ice) and then pour it into the tank when temp gets too high??

  13. avatar

    Hi Rudra, As long as you are not adding ice to the tank or adding too much at one time, that should be fine.

  14. avatar

    Amazing post and also very informative. Awesome tips that you have mentioned here. Thanks for sharing.

  15. avatar

    Do you think it would be okay if I got a cup of tank water, freeze it and put the ice in the filter? The water is at 80 degrees and I’m worried. You said that it isn’t good if fish eat the ice, so is it okay to put it in the filter where he can’t reach it? I have a hang-on-the-back filter btw.

  16. avatar

    Hi Molly, How large is the tank? What kind of fish are they? Have you tried just a fan across the surface? 80F is fine for most tropical fish.

  17. avatar

    I have a comet goldfish (just one) and the tank is 29 gallons. I don’t have a fan that I can suspend over the surface. The room he’s in has a ceiling fan, but my house gets dusty easily and I’m worried about too much dust getting in the tank, so I’d like to keep the hood on. I also I can’t turn on an AC because we’re going through a remodel. I’ve been using ice and the water is still high. About 80 – 82 degrees. He’s been having problems recently and I think the heat is stressing him out more. 🙁

  18. avatar

    Hi Molly, A 29-gallon tank is small for a Comet Goldfish. If it is already having problems, I would definitely recommend testing the water since higher temperatures can make poor water conditions even more harmful. I wouldn’t recommend putting ice loose in the filter but you can try freezing a small water bottle or small sealed bag of water and putting that in the overflow to help cool the water as it flows through. For a tank that small, I wouldn’t use more than maybe around 8 ounces of ice at a time. Removing or at least venting any hood over the tank would make a big difference as well, as would turning off any heat-producing lights like fluorescents (anything other than LEDs).

  19. avatar

    I do agree that 29 gallon is a bit small, but it is much better than the 15 gallon he had before. I can’t get him a new tank because we’re low on funds and he was just moved into the 29 a few moths ago. I thought the problems might be from water quality, but when I get it tested, it reads as normal and I use good conditioners and half the time use bottled water for tank changes and he is still having problems.
    We’ve been having a heat wave and during the day his tank reaches up to 82 and at night goes down to 76. I think the sudden rise and fall is stressing him out more and he’s surface gulping. I’ve been using different methods for cooling, but nothing is helping and I think the only thing I can do is wait for the heat wave to pass or for the remodel to be done. 🙁

  20. avatar

    I have a 20 Gallon tank and live in Alabama where temps can reach around 100 in the summer time. What should I use? I have seen chillers for large tanks but nothing for a 20 and I am worried about summer time. lol

  21. avatar

    Hi Carrie, How hot does it get in the room where the tank is located? As long as the tank is inside and the room temperature isn’t extremely warm, I wouldn’t expect the tank to get the same temperature as outside. That said, there are smaller chillers that could be used on a smaller tank (for example, the Aqua Euro 1/13 HP Max Chill Aquarium Chiller) and the tips listed in this article should help you.

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