10 Reasons Fish Stay At The Top Of The 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!

Key Takeaways

  • Fish stay at the top of the tank for various reasons, including low oxygen, high ammonia levels, temperature issues, swim bladder disease, overcrowding, species-specific behavior, learned behavior, insufficient lighting, and the presence of new fish.
  • The solution depends on the reason why your fish stay at the top of the tank, so it’s important to know the cause.
  • Some fish are natural surface swimmers, and this behavior may be normal for them.
  • Preventive measures include ensuring a cycled tank, using a suitable filter, maintaining proper temperature, good lighting, and avoiding overcrowding.

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.

Lack of OxygenFish swimming at the top of the tankAlter filter current to increase surface disturbance. Add an air bubbler for oxygenation.
Introduce live plants for oxygen production
High Ammonia LevelsGasping for air, change in gill color, loss of appetiteTest water and ensure ammonia, nitrite, and nitrate levels are in check.
Perform a water change.
Add an ammonia neutralizer Include ammonia removal media in the filter
Water TemperatureFish staying near warm areas due to uneven heatingAdjust heater placement for even heating
Add an extra heater for larger tanks
Position a heater behind the filter
Consider relocating the tank for stable temperature
Swim Bladder DiseaseDifficulty swimming, sinking, swimming sideways, floatingAddress constipation through fasting
Try an Epsom salt bath
Overcrowded TankFish seeking refuge at the top due to crowding and aggressionRelocate some fish to a separate tank
Remove bullies
Add more plants and hiding spots
Surface Swimming FishCertain species naturally stay near the topObserve to ensure fish remain healthy
Learned BehaviorFish associate the top of the tank with feeding timeConsider feeding at different tank levels
LightingInsufficient lighting can cause disorientationUpgrade tank lighting for better visibility
New FishNew fish may stay near the surface due to adjustmentKeep lights off initially to reduce stress
Monitor water parameters

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!

Reddit User u/Ok_Ad138 shows perfectly what a lack of oxygen looks like


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.

Pawfly Aquarium 40 GPH Compact Air Pump Quiet Oxygen Aerator Pump with Air Stone Airline Tubing and Check Valve Accessories for 5-20 Gallon Buckets and Fish Tanks
  • Compact & Light: Measures 3.3″ L x 1.8″ W x 1.6″ H. Ideal for those who are tight on space. Suitable for 5 – 20 gallon fresh and marine fish tanks and aquariums.
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!

Large fish tank with tropical coral reef

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.

And remember, sometimes ammonia can even occur in your tap water. So if that’s the case, you’ll need to try some of the options below.

ammonia in tap 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.

betta care facebook group

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.

User Recommendations:

As well as the following, after scouring forums, I found this thread, that had some great alternatives (although I haven’t tested them):

  • Indian Almond Leaves
  • Peas (For Non Carnivores)


  • Bettafix
  • Melafix

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

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.

Naturally Surface Feeders

And in some cases, it’s simply that your fish are surface feeders, so they’ll want to spend most of their time near the top of the tank

Remember, over millions of years, some species have adapted to feeding at the surface because it provides advantages like access to more abundant food resources like insects and floating plants.

Ever notice how a Betta fish has an “upturned” mouth? This evolutionary adaptation helps them gulp air and food at the surface.

A Problem With The Lighting

It might also be the case that there’s not enough lighting in the tank. If there’s not enough light in the tank then your fish may become disoriented and spend more of their time near the top of their tank where they can see better.


Of course, the easiest way to fix lighting is to buy better lights for your tank. As a rule of thumb, fish are going to need 1-2 watts per gallon of light, so if your current setup doesn’t have this, then it’s definitely time for an upgrade!

You’re Dealing With A New Fish

And lastly, it could be the case that you’re dealing with a new fish. When fish are in a new environment, they’re going to be sensitive to the water parameters until they’ve adjusted. This can result in abnormal behavior like the fish staying near the surface of the water.

As well as this, if your tank already has a lot of other fish in it, then they may feel safer near the surface of the water.


There aren’t many solutions for this one. I would recommend keeping the lights off for the first few days if this is the case to help reduce the stress they’re feeling, and keeping an eye on the water parameters to make sure they’re not swinging to wildly.

10 reasons your fish is at the top of the tank! (2)

How To Prevent Fish From Swimming Near The Top

Fortunately, there are plenty of things you can do to stop your fish from swimming near the top of the tank from the get go. So make sure when you’re caring for fish you’re keeping these things in mind.

Keeping Your Tank Clean

To keep your fish happy and healthy, make sure to give their home a good scrub at least once a month. It’s like giving your fish a clean place to live and reducing the chances of them getting sick. Get rid of the decorations, vacuum up the gunk from the bottom, and make that tank sparkle!

And don’t forget to change out about a quarter of the water twice a month. This freshens up the environment and gives your fish room to grow and thrive.

Welcoming New Fish

If you’re adding new fish to your existing group, always be cautious. Place them in a separate tank for a couple of weeks first. This acts as a quarantine period to ensure they don’t bring any unwelcome diseases with them. You can set up a smaller tank for this purpose.

Cycle Your Tank

Always ensure your tank is fully cycled before adding new fish. A well-cycled tank should have zero ammonia in it which is going to keep the stress level of any new fish low!

When you’re checking the water parameters, just make sure you’re using a reliable testing method.

API FRESHWATER MASTER TEST KIT 800-Test Freshwater Aquarium Water Master Test Kit, White, Single, Multi-colored
  • Contains one (1) API FRESHWATER MASTER TEST KIT 800-Test Freshwater Aquarium Water Master Test Kit, including 7 bottles of testing solutions, 1 color card and 4 tubes with cap

Make Sure You’re Using A Good Filter

Every fish tank needs a filter to remove waste aerate the water. So make sure you have a filter that’s suitable for your tank size and that it’s in tip-top shape. Regular maintenance can’t be ignored; it helps in the long run.

As a general rule of thumb, you want your filter to be able to turn over 3-4 times the amount of water in the tank per hour.

Tetra Whisper IQ Power Filter 20 Gallons, 130 GPH, with Stay Clean Technology
  • QUIET AQUARIUM FILTER: The Tetra Whisper IQ Power Filter with Stay Clean technology contains a sound shield for quiet filtration less than 40 dB.

Maintain Optimal Temperature with a Heater

Temperature consistency is vital for your fish’s well-being. Fish are cold-blooded so their body temperature is determined by the warmth of the water they’re in.

With this in mind, you should aim to add a heater to your tank which is 5 watts per gallon of water.

Tetra 26446 HT Submersible Aquarium Heater With Electronic Thermostat, 100-Watt,Multicolor, 10-30 Gallon
  • All Tetra HT heaters have indicator lights to let you know when the heater is on. It will be red when heating and green when the proper temperature has been reached.

Use Good Lighting

And make sure that you’re keeping the tank well lit (but not too well lit) so that your fish aren’t going to get disoriented when they’re swimming around.

Avoid Overcrowding

Last but certainly not least, avoid overcrowding your tank. More fish mean more waste and a higher demand for oxygen, both of which can stress out your aquatic pets and send them to the top for relief.

And of course, the more crowded the tank is the more likely it is that bullying will happen, or just stress of too many fish for more timid tank mates.

A good rule of thumb is to stick to the one inch of fish per gallon, however, remember, this does vary depending on the fish you’re keeping.


Here are some frequently asked questions that people have about why their fish is staying at the top of the tank.

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!

Why Is My Fish At Top Of Tank But Not Gasping?

If your fish is at the top but not gasping for air then it’s probably dealing with a less serious issue like mild stress. However, if you notice other symptoms like bloating and trouble swimming, then it could be swim bladder disease.

Why Is My Fish Floating At Top Of Tank?

If your fish is floating at the top and appears lifeless, it’s a serious concern that could indicate severe illness or even death. Immediate action is required.

You’re most likely dealing with swim bladder disease or a fish that’s on deaths door, so you’ll need to address the issue immediately.

How Do I Fix Low Oxygen In My Fish Tank?

To increase oxygen levels in your fish tank, add an air stone or a secondary oxygen source. Adjust your filter for better water flow and surface agitation. Remember plants can also help, as they release oxygen during photosynthesis.

Can Fish Recover From Lack Of Oxygen?

Yes, fish can recover from a brief period of low oxygen if addressed promptly. Once you’ve increased the tank’s oxygen levels by adjusting the filter or adding an air stone, the fish should start to behave normally. However, prolonged lack of oxygen can cause permanent damage or even be fatal so immediate action is crucial.


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!


About the author

Hey! I'm Antonio!

Betta fish keeper for over 6 years now! Since owning a betta I've also housed all kinds of tropical fish, and have seen all manner of problems and how to look after them!

If you need any advice you can always message me or better yet join the Facebook group where a community can answer your questions!