7 Reasons Fish Stay At The Top Of Tank (& What To Do)

Are you wondering why your fish are staying at the top of the tank? Sometimes it’s a cause for concern, and other times you won’t need to worry at all. However, being able to differentiate between whether it’s fine or not is going to be the difference between whether your fish live or die.

In this article, not only are you going to find out all the different reasons your fish could be staying at the top of the tank, but you’ll also learn what you can do to fix the problem as well!

So keep reading to find out everything you need to know!

Why Are You Fish Staying At The Top Of The Tank?

Here are all the different reasons your fish could be staying at the top of the tank and, more importantly, what to do about it! Remember, it can also be multiple reasons that are causing your fish to be at the top of the tank, not just one.

Not Enough Oxygen

Lack of oxygen in the water is one of the main factors that can cause a fish to stay at the top of the tank. Oxygen tends to rise in water, so your fish may begin swimming to the top of the tank when there’s not enough.

Things like the water not moving around enough, the temperature rising, and the tank being overcrowded can all be reasons for lack of oxygen in the tank!


Fortunately, if there’s a lack of oxygen in the tank, there are a few things you can do to aerate the water more and help your fish breathe again!

Move The Filter Current

Altering your tank’s filter current should be your initial course of action. Aiming the filter so that it disturbs the surface of the water more will increase the amount of oxygen entering the tank. In fact, the result is so rapid that it’s going to be the best short-term solution.

Just be careful that you don’t end up disturbing the fish in your tank. Some fish don’t like strong currents, so it may stress them out.

Try An Air Bubbler

Adding an air bubbler to your tank is another one of the EASIEST ways to increase the amount of oxygen. They are reasonably priced, and setting them up is easy as well. And if you don’t like the look of them, there are also several ornaments you can use to conceal them in order to maintain the illusion that the tank looks natural.

Air bubblers will add oxygen to the water, and while they’re usually unnecessary, they won’t get in the way either.

Large fish tank with tropical coral reef
Add Live Plants To The Tank

Finally, you can also add plants to the tank too. Similar to trees, plants will boost the tank’s oxygen levels and eliminate CO2.

Anubias nana, java moss, java fern, and marimo moss balls are all excellent possibilities if you’re not sure what plants to include. However, if you’re feeling more adventurous, hornwort and anacharis provide some of the best oxygenation!

The Ammonia Levels Are Too High

Another reason that fish could be staying at the top of the tank is when the ammonia levels are too high. Even if the water looks clean, the ammonia, nitrite, and nitrate levels could be rocketing, causing your fish to suffer and increasing the risk of ammonia poisoning.

When there’s too much ammonia in the tank, you may also notice the following behavior from your fish as well.

  • Gasping for air.
  • Change in gill color.
  • Red streaks along the body and fins.
  • Inflamed eyes and anus.
  • Loss of appetite.
  • Lethargy


Before anything, you should test the water in your fish tank. Anything above 0ppm is too much. On top of ammonia being at 0ppm, you should also make sure that the nitrite levels are at 0ppm and the nitrate levels are below 20ppm.

If you don’t know how to test the water, then you’ll need an API Master Test Kit, which allows you to test the Ammonia, nitrite, nitrate, and pH levels in your tank.

Once you’ve tested the ammonia levels and they’re too high, then do the following:

Perform A Water Change

A water change should be done right away when the levels of ammonia, nitrite, or nitrate are excessive. Performing a 50% water change while extreme is going to remove most of the ammonia from the tank while also diluting the remaining amount with fresh water.

Add An Ammonia Neutralizer

Sometimes only changing the water isn’t enough to lower the ammonia levels, so if the ammonia levels are still excessive, you might also need to add an ammonia neutralizer to the tank too. I like to use API Ammo Lock; however, you should use whatever’s easily available to you.

Add Ammonia Removal Media To Your Filter

If your filter has room, you can also include some ammonia removal media to it. Then ammonia will be removed when water flows through the filter, in turn reducing the overall amount of ammonia in the tank.

Aquaclear Ammonia Removers are a great choice if you’re unsure of what ammonia removal media to purchase.

The Water Temperature

If there’s a problem with the water temperature, then it can also cause your fish to stay near the surface of the tank too. Warm water rises while cold water sinks. So your fish may end up trying to stay in the warm water if the rest of the tank is too cold.


Fortunately, if the tank is too hot or cold in some places, there are a few things you can do to fix the issue.

Move The Heater

The heater can sometimes warm up one region of the tank well while providing an insufficient amount of heat in the other areas, so moving it is the first thing you should try to do. Doing this can help you ensure that the tank is getting an equal amount of heat across all the water.

Add An Extra Heater

The size of the tank may also determine whether you need an additional heater or not. When the tank is too big, one heater just won’t be enough to heat all the water, so using multiple is the only solution.

And don’t worry about overheating. As long as both heaters are set to the same temperature, they’ll both turn off when the water reaches the designated temperature.

Place A Heater Behind The Filter

A heater can also be positioned behind the filter. By doing this, the heater will warm the water that is being forced through the filter. The heated water will then circulate throughout the tank, keeping it at a warmer temperature.

Relocate Your Tank

Finally, you might need to relocate where your tank is. You should move your tank to somewhere that’s a bit warmer and where the temperature is constantly stable.

Swim Bladder Disease

Fish have a lot more difficulty swimming when they’re suffering from swim bladder disease. As a result, they frequently struggle to maintain their position, sink to the bottom of the tank, swim sideways, and even float to the top.

It’s unlikely that your fish has swim bladder disease if you notice they can swim to the top of the tank on their own; but, if you see that they seem unable to escape from the bottom or top, no matter how hard they try, you may need to treat them for the condition.


If you want to treat swim bladder disease in your fish, then you should try the following:

Treat Them For Constipation

Swim bladder disease is frequently brought on by overeating and constipation; thus, by addressing these conditions, swim bladder disease can also be cured.

You can treat these two conditions most easily by fasting your fish for a few days. By doing this, you give their stomachs a chance to be entirely emptied, which can often fix the issue.

You can also try adding some daphnia to your tank if fasting alone is unsuccessful. Daphina contains a lot of fiber that your fish can digest (unlike plants), which will aid in restoring their digestive system. (If you have herbivore fish, you can also try a cooked deshelled pea.)

Epsom Salt Bath

Giving your fish an Epsom salt bath can frequently be a helpful suggestion in situations where simply fasting isn’t sufficient to cure swim bladder disease.

The following steps must be taken in order to give your betta an Epsom salt bath:

  1. Mix 1 tablespoon of Epsom salt with half a gallon of conditioned tap water in a clean container.
  2. Once the Epsom Salt has dissolved, add half a gallon of your aquarium water into the container.
  3. Replace the water taken from your aquarium with conditioned tap water, which is the same temperature as your aquarium.
  4. Leave your betta in the bath for 10-15 minutes. If this hasn’t cleared his constipation in that time, put him back in his tank.
  5. Continue monitoring your betta throughout the day to see if he’s excreted or he’s swimming better.

The Tank Is Overcrowded

Sometimes, it can be the case that the tank is just too crowded. Not only will an overcrowded tank get dirty faster, resulting in the tank becoming dirty fast, but it can also cause the oxygen levels to drop too much. As well as this, some fish may feel threatened or bullied in an overcrowded tank, so they’ll attempt to stay at the top or bottom of the tank, away from other fish.


If your tank is overcrowded, there are a few things you can do to fix the issue. Where possible, moving some fish into a separate tank is the best choice. However, this can’t always be the case. When you can’t move your fish, then you should try the following:

Remove Bullies

If your fish is being bullied, they may also stay at the top of a crowded tank. This can frequently be caused by larger, more aggressive fish, but it can also occasionally be tiny fish, such as neon tetras, which can repeatedly nibble at a fish’s fins.

The best course of action, in this case, is to remove any bullies from your tank and either gift them to a friend or put them in another tank.

Add More Plants

Another great choice is to increase the number of plants. This will give your fish a lot more hiding spots with the addition of more plants, and a lot more lines of sight will be broken, reducing the chance of bullying occurring. Additionally, plants assist in maintaining optimum water conditions, which helps keep ammonia levels low and oxygen high.

Hiding Spots

Along with plants, decorations like driftwood, stones, and ornaments can give your fish lots of places to hide. Again, give your betta a much-needed rest and break!

Your Might Have A Surface Swimming Fish

Sometimes, it’s simply the case that your fish could just be surface swimmers. For example, bettas love to stay at the surface of the tank. As well as this, zebra danios, guppies and hatchetfish can all be seen at the surface of the water at times as well.

However, even if a fish is meant to be staying at the top of the tank, keep an eye on them to make sure they remain healthy.

They’ve Learnt To Swim To The Top

And lastly, it could just be the case that your fish have learned to swim to the top of the tank. Over time, fish can begin to associate seeing you or a light turning on with dinner time. When this is the case, they may go to the top of the tank because they’re expecting food.

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Why Is Your Fish At The Top Of The Tank After A Water Change?

If a fish has gone to the top of the tank after a water change, there could be a few reasons behind it.

  • First of all, if you didn’t match the temperature of the water to the tank, you could have dropped or raised the temperature dramatically.
  • Secondly, the water change may have stressed the fish out and resulted in erratic behavior occurring.
  • If you cleaned the gravel and filter, you might be on top of a water change; you may have started a mini-cycle. This will result in an ammonia spike which could be making your fish sick!


As you can see, there are a lot of reasons that your fish may be staying at the top of the tank. And fortunately, in most cases, there are also a lot of solutions! If you liked this article, make sure you check out the rest of the website! Otherwise, have a great day!