How to Keep Your Fish Cool

keep fish cool under umbrella

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We’re in the midst of some crazy temperatures right now and we have a lot of fish owners concerned about their elevated water temperatures. Here are some tips to keep your fish cool when temperatures rise.

Why is water temperature important for fish?

Remember that fish are ectotherms, meaning their body temperature is almost identical to their water temperature. All fish species have their ideal temperature range, and what is the best range for a goldfish is very different from a cichlid or clownfish. When fish are outside their ideal thermal range, they start to have issues compensating within their bodies, leading to stress and secondary disease outbreaks. At extreme temperatures, either too cold or too warm, they can become unable to compensate and die.

Why is it important to keep my fish cool?

It totally depends on the type of fish you keep, but every fish will have an upper temperature tolerance. Tropical, marine fish tend to do the best in warmer water, but have a very low tolerance for cold. Koi and goldfish, with some of the largest temperature tolerances, start to have issues when their water gets up in the 80s (F). Don’t forget that as water temperatures rise, they hold less oxygen, so be sure your tank or pond has plenty of water features to provide fresh oxygen if your water gets warm. Not sure what temperature your fish can handle? Check out this resource.

How do I know if my fish are too hot?

The best way to test if your water is too hot is to watch your fish. If you see them struggling to swim, not interested in food or have increased respiratory rate or effort, check your water temperature! Bacteria and parasites like a warmer environment, so you may see an increased rate of infection or secondary signs, such as kidney and gill malfunction (typically called “dropsy”). A reliable thermometer for your tank or pond is the best method of seeing if your temperature is appropriate. If it is too cold, you may need a heater, but if it is too warm, you need to take immediate steps below to bring relief to your fish.

How to Keep Your Fish Tank Cool

If your fish tank temperature is starting to rise, here are some tips for keeping your aquarium fish cool:

Add a frozen water bottle

The easiest thing to do for a small system is to take a empty bottle of water, remove all the stickers and adhesive, fill it up halfway, stick it in the freezer and then let it float in the top of your tank. Depending on the size of your tank, you may need one or two. Keep a close eye on your temp to make sure you do not swing it too low! Adding ice can also help if you lose power and cannot rely on the other methods listed here. If you are without power for awhile, be sure to check out our Disaster Planning Guide for Fish.

Add an aquarium fan

Yes, they make fans for aquariums! This can help blow cooler water across your tank’s surface and bring down the water temp. If you have an air conditioner nearby, this may super cool your water very fast, so be sure you keep a close eye on your water temp.

Cool down the room

If possible, try to keep your fish in the coolest area in your house. This means away from open windows and any areas where the sun may cook the internal room temp. If you have a colder spot in your house, are you able to move your fish and their tank to that room? How about a temporary tank in that room? Be sure to bring your filter to avoid New Tank Syndrome!

Have a tiny tank? Add a couple of ice cubes

For small betta and nano tanks, a couple of ice cubes may be all you need to maintain cooler water. Keep in mind that if you do not condition your water prior to turning it to ice, it may release toxic chlorine into your tank as it melts. So, either treat your water with a conditioner before turning it to ice or add some more conditioner to your tank when you add your ice.

How to Keep Your Fish Pond Cool

Outdoor ponds, exposed to the elements and significantly larger, are harder to control. Here are our best recommendations:

Add an umbrella

Adding some shade via a portable umbrella is a quick and simple fix for many fish ponds. You may already have one available that you can move into position. Try to shade the deeper areas of your pond so your fish can stay cool. You may need to move your umbrella throughout the day as the sun moves or have multiple umbrellas depending on the shape of your pond.

keep fish cool under umbrella
Offset umbrellas such as this are great at keeping fish ponds cool!

Add some plants

Pond plants provide lots of benefits to your pond, including shade and blocking the sun from your water surface. Just be sure to quarantine them properly if they were previously kept with fish and beware your fish may enjoy snacking on them.

Add some ice – don’t forget the dechlorinator!

Just like with our small tanks, you can add ice for a temporary fix or sudden temperature spike in a large pond. You may need a few bags depending on how warm your water is and how large your system is. If you do lose power, this can also help keep things cool until you are able to get back flowing again. Check out our Disaster Planning Guide if you are without power for awhile.

Cover filtration equipment

Most pond filtration equipment is contained within dark, plastic shells. These can heat up quickly and not only super heat your pond water, but also become at risk for failing. Be sure to keep your equipment cool so you don’t have to worry about a power outage.

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2 thoughts on “How to Keep Your Fish Cool”

  1. I have two blood parrots in a 30 gallon tank. One of them has swim bladder so he’s in a breeder thing. The other one nudges at him some time. Would he kill the sick one?

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