Skip to main content

Check these 3 things immediately if fish are swimming at the top of the tank

Here's what might be causing fish to swim at the top of their tank

Diving into aquarium ownership means learning all sorts of fun new things about fish — how to feed, clean, and decorate for starters. On the flip side, you need to know what to look for to determine if something’s wrong. Unlike with a dog or even a hamster, you can’t get a good sense of a fish’s feelings from petting him. Instead, you have to pay attention to the tank as a whole and think of it as one ecosystem with lots of different pieces. That means keeping track of fish, plants, water, and filters.

If you find your fish swimming at the top of the tank, you should take action right away. Here’s what to do when your fish spend too much time at the surface.

Fish swim around in a tank with a bubbler

What does it mean when your fish swim to the top?

Usually, your fish go to the surface when they’re not getting enough oxygen. Unlike you, they use their gills to breathe the air that’s already in the water. However, in some circumstances, there’s not enough oxygen in the tank for all the fish to breathe easily. To combat this, they swim up to the surface, where there is oxygen-rich water. You may notice some gasping or other signs that they’re not well while they are up there. 

Mom and baby look into fish tank

What to do when fish stay at the top of the tank

While it’s fairly serious if your tank-dwellers can’t breathe well, there are a few steps you can take to fix the problem straight away. You might also need to rethink your setup, once the initial emergency has passed.

Do a water test

You should be performing water tests regularly, including every time you change out some of the water. It’s important to check nitrates, pH levels, and ammonia to see if anything is out of whack. This usually happens when you have a bigger issue in the aquarium, such as too many fish. It could also be a sign that you’re overfeeding and the excess food is rotting at the bottom. You may need to take quick action with a partial water replacement and use conditioners to help bring your chemical levels down. In the long term, you’ll have to find a way to reduce waste; usually feeding less will do the trick. Also, look into adding live plants which will produce oxygen and remove excess nitrogen compounds naturally. 

Check the filter

Your filter will help to remove some of the waste from your tank, though frequent cleaning and water changes are still very important. Additionally, filters help to increase the amount of oxygen in the water by stirring up the surface and allowing the liquid to flow through the air consistently. Add more elements (such as a bubbler) to increase the levels of oxygen, permitting the fish to breathe more easily. Examine your filter for any breaks and replace sponges or other old pieces. Lastly, make sure your filter system is big enough for your tank. You may need to purchase a larger one if you’ve recently added fish.

Install a thermometer

Yup, you read that right. Water temperature makes a big difference to the oxygen level in your fish tank because cold water holds more dissolved oxygen than warm water. That means you need to be particularly careful when the room temperature rises, either because of summer or your tank heater. You should track the climate all the time anyway to ensure it stays consistent.

If your fish are congregating at the top and your notice an uptick in degrees, try cooling the room or turning down any heat sources. You don’t want to make sudden, drastic changes. Adjust the temperature incrementally so as not to shock your fish, and never let the water temperature fall below the recommended range. Move the tank if necessary, especially to provide better ventilation.

Remember that one of the biggest concerns for aquarists is overcrowding. We recommend starting with one tank and a small school to manage so that you get the hang of it first. Once you feel confident, you can branch out. This includes carefully moving fish to a new tank if you find you have too many (perhaps they have multiplied), or if they’ve gotten too big. Pretty soon, you’ll wind up with multiple tank systems and plenty of animals to care for.

Goldfish in water

The bottom line on fish tanks

It can be tempting to dive into this hobby head-first and then wind up in deeper than you expected, but with a lot of care and a little bit of research you will find yourself better prepared to look after your little scaled pals and know what to do should a problem arise. 

Editors' Recommendations