Fish Staying at Top of Tank and What to Do About It

Last Updated on September 21, 2021 by cmoarz

So your fish is staying at the top of the tank and you are not sure what to do.

Don’t worry, I’ve got you covered!

In this article, I will talk about the reasons why your fish may be doing this and what to do about it.

I will also explain each problem, talk briefly about how common it is, and give you some helpful tips on how to deal with the issue.

We’ll start from the top and work our way down:

Fish staying at top of tank what to do

Fish swimming at the top of the tank isn’t an uncommon problem to have. Sometimes, it’s a perfectly normal expected behavior based on the species of fish you have. Sometimes it’s not.

This article assumes you’ve already done your due diligence looking up the type of fish you have a problem with and figuring out if it’s just natural behavior. So we will only go into the things you should be worried about, How to diagnose the issue and how to solve the problem.

Low oxygen levels

Dissolved Oxygen and Low Oxygen Levels

  • Signs of low oxygen:
  • Labored breathing
  • Constantly coming up for breath
  • Gasping for breath
  • Wide-open mouth at the surface of the water
  • Always staying at the top sticking its head out of the water constantly
  • Other fish have died
  • Adult fish seem more affected than fry
  • All the fish in the tank are showing abnormal behavior.
  • Some fish show normal behavior, Mostly fish like bettas or corydoras, but other fish’s behavior is that of what’s listed above, with top tank gasping.
  • Fish won’t go to the bottom when they normally do and prefer to hang out in the middle or upper regions of the tank,
  • Other factors

This is one of the most common reasons why your fish will swim at the top of the tank. If there isn’t enough dissolved oxygen or if the fresh oxygen levels in your tank are too low, you’ll notice that your fish will be at the surface a lot more frequently than normal. To put it plainly, They can’t breathe.

Poorly oxygenated water or too many fish in the tank with not enough fresh oxygen coming into the water from an air stone or turbulent filter can easily cause dead fish, fish gasp, and fish to hang out at the surface area of the tank trying to breathe.

If you don’t have sufficient oxygen in the tank, fish will end up suffering greatly and maybe dying in large numbers if they are super sensitive to less oxygen. This can also signal an increase in carbon dioxide. Carbon dioxide is heavier than oxygen, so it will accumulate at the bottom of the tank and may affect bottom aquarium fish before it affects top aquarium fish.

With that said, You can never have too much oxygen, so get as much oxygen into the tank as possible. This is very easily achieved by getting a good filter and setting it up high enough to cause turbulence that mixes in oxygen. Some filters offer oxygenation as a feature as well.

If your tank is low in oxygen, this can also be easily fixed by getting an air pump, tubing, and an airline airstone. Place the airstone in one corner of the tank where you want to add more oxygen and run the tube so that it is cleverly hidden behind some decor or driftwood.

An air pump should be run 24/7 to be sure enough oxygen is reaching the tank. If you have a very large tank, you may need more than 1 airstone to get enough oxygen dissolved into the water.

Luckily, as the most common issue people face with their fish, it’s also the easiest to fix. Getting dissolved oxygen into the water and increasing oxygen levels is one of the easiest first steps you can do.

And hey, Even if your fish aren’t showing signs of low oxygen levels, it’s always good to have an airstone or another method of adding dissolved oxygen to the tank anyway. This is especially true for species of fish who can’t breathe at the surface properly and almost always require oxygen intake from their gills.

You should also consider adding live plants. Live plants will give off oxygen and prevent low oxygen level from happening if you’ve got enough of them.

Water Temperature, too hot too cold

Water Temperature

While slightly rarer of an issue as the wrong water temperature usually have 1 of 2 outcomes. The fish will die very very quickly, Or just become very very sluggish. There are a few exceptions, such as an auto water changer breaking down and pouring in very hot water which will cause the fish to dart around in pain and try to get as far away as possible Although this is rare with a proper setup.

Another exception is when your aquarium water columns are different tempretures. The larger your tank is, the more often this can become a problem with a lack of water movement. The bottom aquarium water column will have more cold water, and the top will have warm water. Because of lack of water movement, the 2 rarely mix.

When a fish swims from a warm water column to a cold water column, the colder temperatures can cause shock. This will keep the fish at the top of the tank gasping for air and looking like it’s trying to swim but isn’t going anywhere. These strange swimming patterns are easy to spot.

If a fish in this situation is in a large enough tank, they may pass out in the warm area between water columns and appear dead before eventually waking up later when the temperature changes have evened out again.

This issue can be prevented by having a heater in the tank with proper water movement and flow circulating threw out the entire tank and all water columns.

For no current tanks, which some fish require, A bottom tank heater, Or an in-substrate heater can often fix the issue of cold water at the bottom column.

Water Parameters

Poor water quality may also be a reason for fish to hang at the surface.

Water can be crystal clear but also poisonous, and ammonia generated by fish and nitrite, a by-product, are potentially fatal at any concentration above zero. Always check pH levels as well.

Test the water for ammonia and nitrite using test kits, or install a Seneye monitoring device to notify you if ammonia is present.

If ammonia is present you will need to revisit your tank cycle and be sure to do a none chlorinated water change.

To transition the toxic ammonia into a less harmful ammonium, change half of the water and add Ammonia remover.

Examine the aquarium as a whole and consider why ammonia was present. Was it because of a new tank that had been poorly prepared, or simply because there were too many fish in it? Did it have enough time to fully cycle? Consider adding some API quick start into the water and filter to help it along.

Is it possible that the fish have been overfished and that there is a decaying fish somewhere decomposing?

Has the filter gone off owing to a power outage?

Is something obstructing the filter? Or did you just replace the old media with fresh, eliminating all of the helpful bacteria in the process? As quickly as possible, add new filter bacteria to restore ammonia levels to zero.

Do not use chlorinated water. Be sure all chlorine has been removed with a dechlorinator/water conditioner. If your water has chloramine instead of chlorine, Be sure to buy the appropriate conditioner or chloramine filtered water. You can buy a filter specially designed to give filtered water without chloramine, although it’s expensive unless you have large setups or many tanks.

Conditioners are often cheaper and easier to use. Just be sure to get the right one for your water.

Until your tank is fully cycled, it’s important to test every day. Test consistently and often.

Other factors worth mentioning

  • Low lighting. Low lighting can cause issues for some fish varieties.
  • Loud noises can sometimes startle fish. If your filter is too loud, some fish varieties may be skittish and chill at the surface (or at the bottom hiding).
  • They’re simply waiting to be given food. If they don’t show any signs above, It could be they are just hungry and want you to give them some food. It’s normal to come to the surface for food if that’s how you feed them.
  • More fish than the tank can handle, and it’s become overcrowded. Even if oxygen isn’t an issue, overcrowding with more fish than the tank is comfortable with may push fish to the surface. Avoid an overstocked aquarium.
  • New fish might be bullying old fish. If that’s the case, Either the new fish or the old fish may try to escape by being at the top of the water column (or the bottom).
  • Disease. A fish may have a disease that makes it struggle to swim or breathe, and eventually forces it to float at the surface. If a fish struggles inspect for visible signs of injury or disease. Things like extra mucus production, burns or open wounds, Bloat, etc.


When in doubt, Add oxygen, Do a partial water change or a full water change. Keep an eye out for algae, although algae usually produce oxygen and isn’t always a bad thing to have. Keep an eye on the temperature, and be sure to have something to monitor temperature all the time. This means something with a probe for the bottom of the tank too on larger tanks and not just something that hangs on the side.

Check for illness and water quality, ammonia, pH levels for your fish species, check for ammonia burns on gills, and watch out for gasping to breath which indicates more oxygen is needed.

Buy a heater if the temperature is too cold, Use ice cubes and set up aquarium fans if the temperature is getting too hot, and always keep an eye out for temperature changes.

Don’t overfeed, buy a good filter media to quickly cycle your tank without having to use chemicals, do frequent partial water changes if necessary, and always watch the ammonia levels in the water.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!