FishTankWhy are my fish gasping at the surface?
Fish hanging at the top of the tank and gulping are usually telling you something is wrong with the water. Here's how to find the cause, and what to do right now.
First, is it actually a problem?
Bettas and gouramis breathe air from the surface as well as through their gills. If they swim up, take a gulp and swim away, that's normal. Fish also crowd the surface when they expect food. Worry when several fish hang at the top for a long time, breathe fast, or look stressed.
What to do right now
- Test ammonia and nitrite. Either one above zero can damage gills and make fish struggle to breathe.
- Check the temperature. Warm water holds less oxygen, and a stuck heater can overheat a tank fast.
- Get the surface moving. Point the filter outflow up so it ripples the surface, lower the water level slightly so the outflow splashes, or add an air stone. Oxygen gets into the water at the surface.
- Do a water change of about 30–50% with conditioned, temperature-matched water if ammonia or nitrite is above zero.
- Hold back on food for a day while you find the cause.
The common causes
Low oxygen
Too little surface movement, too many fish, warm water, or a filter that has slowed down because it's clogged. It's often worst early in the morning, after a night without plants making oxygen. Fix it with more surface movement or an air stone, and clean the filter if the flow has dropped.
Ammonia or nitrite
Common in new tanks that haven't finished cycling, after adding a lot of fish at once, after overfeeding, or after something has died in the tank. Do water changes until both read zero, and feed lightly for a while.
Water that's too warm
Above about 82°F, oxygen levels drop and fish breathe harder. Check the heater, keep the tank out of direct sun, and use a thermometer you trust.
After medication or a big change
Some medications lower oxygen levels. Add extra aeration whenever you treat the tank.
When to worry
Act fast if fish are breathing very quickly, have red or inflamed gills, are lying on the bottom, or if fish start dying. Do a large water change straight away, then keep testing.
Helpful for this problem
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- Test kitAPI Freshwater Master Test KitCheck ammonia and nitrite first. They are the most common cause.
- Air pumpTetra Whisper air pump, 10–30 gallonsRuns an air stone to add oxygen and surface movement.
- Air stone kitShappy airline tubing and air stone setTubing, air stones and check valves to connect the pump.
- ThermometerZacro digital thermometer (2 pack)Make sure the water isn't too warm.
- Water conditionerSeachem Prime (500 ml)Treat the new water for an emergency water change.
Related: How to do a water change · How to cycle a new fish tank · Fish stocking calculator · Ammonia in a fish tank