Why Are My Fish At The Top Of The Tank After Water Change?

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You just performed a water change in your tank and you notice how all the fish swim to the top afterwards. This isn’t a new problem either, it seems to happen after each water change you do. So you are more than likely inquiring, “Why are my fish at the top of the tank after water change?”

The main reason for fish swimming to the surface of the water after a water change is that there’s a lack of dissolved oxygen. You can solve this easily with an air stone and/or oxygen pump. But, it could also have to do with poor water parameters; in which case you’ll have to do further investigation.

However, it’s important to observe your fish since there are some species that enjoy going to the top from time to time. This means it’s not always a bad thing or something for you to have concern over.

Observe the Fish

More often than not, the issue of fish swimming up to the surface of the tank means there isn’t enough oxygen present. 

But, before you go adding more oxygen to the tank, you should inspect all the signs going on and how the fish are behaving.

If they’re moving around and swimming fine, then they could just be at the top because they feel like it. Actually, several species of fish like to hang around at the top of an aquarium.

  • Brown Pencilfish
  • Silver Hatchetfish
  • Bettas
  • Cichlids
  • Golden Wonder ; Clown Killfish
  • African Butterflyfish
  • Furcata Rainbowfish
  • Danios
  • Snails
  • Halfbeaks
  • Gouramis

Fish Showing Signs of Struggle or Illness

When they float to the top and show clear signs of struggle while gasping for air, then the fish may be suffering from hypoxia or swim bladder.

Hypoxia is when the fish doesn’t have any capacity to breathe due to lack of oxygen. This will be especially true if the gills are red.

Swim bladder is an infection common to most fish and causes them to swim close to the surface. They will even appear to swim upside down or sideways. It means they’re constipated due to too much food, overcrowding or not changing water frequently enough.

A good treatment for this is to give the fish oranges, melon or green peas. In more severe cases, you may want to get antibiotics specifically for fish.

Fish Are New to Your Aquarium

However, if your fish are brand new to your aquascape, they could be floating to the surface to get air to compensate for the conditions they lived in at the pet shop.

But, if your fish are long-time residents, then you should measure your water parameters to see how they are after the change.

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Check Water Parameters

Do the standards first, checking for the typical components that make a tank difficult for fish to live in. When nitrites are over 3ppm, nitrates are higher than 100 and ammonia above zero, you will have to do another water change. 

This also includes salinity (for saltwater tanks), pH balance and water hardness.

However, if you just changed the water, then something in the tank is keeping this spike up.

For instance, there could be a dead fish nestled somewhere, like in a hidden area of the substrate or in the water filter. 

Alternatively, you may need to clean out the substrate because there’s too much food sitting at the bottom.

If the parameters check out fine, then measure the oxygen content at the bottom, middle and top of the tank with an oxygen meter.

Read: Why Is My Fish Water Pink? (7 Reasons + How To Fix!)

Aerating the Water

If it reads anything less than 4ppm, you will need to aerate the water. There are four ways to get more oxygen into the aquarium for your fish:

  1. If your water filter or pump is your main source of oxygen, move it through your tank and take another oxygen reading.
  2. Some aquarists suggest drilling hole into pebbles and slowly dropping them into the tank, one-by-one. This helps bring oxygen to the lower parts of the aquarium.
  3. Invest in an oxygen pump along with an air stone (link goes to Amazon). Such devices are the surest way to get air into your tank. While these are pricier, they are a more surefire way to guarantee good oxygen flow.
  4. You could also try adding more live plants (link goes to Amazon) to the tank. This is useful if you have fish that don’t like strong water currents.

However, you want to ensure you don’t over-oxygenate the tank. Too much oxygen can have its own kinds of problems as well. Having said that, understand that most tanks are under-oxygenated.

Water Temperature Is Too High

Another reason why the fish may be swimming toward the top of the tank is that the temperature of your water change was far too warm. It’s imperative that you ensure the water is at room temperature. 

This is because any temperature above 68°F to 70°F will reduce any oxygen molecules present.

Do not take this as an okay to use colder water either. If the water sits below room temperature, it can cause shock to the fish. You will increase the chances of death for more fragile and delicate species. 

Of course, it will all impinge on your fishes’ preferences for water. So, before you change it out, use a thermometer to ensure the water is at the right temperature.

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Final Thoughts

When you find your fish often coming to the surface after a water change, it’s crucial you observe the fish and take readings of the water. In most cases, there isn’t enough oxygen present to keep them happy. But, it could just be your fish likes swimming near the surface. But, if they show signs of struggle, you have to act.

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