When an angelfish starts hanging at the top of the tank, it instantly feels like something’s wrong. Angels are usually confident swimmers that glide around the whole aquarium. So when one suddenly sticks to the top, breathing fast or acting restless, it’s a clear sign that the fish is uncomfortable.
The tricky part is that the tank might look clean and normal, but fish behaviour always reveals the truth before the water does. Here’s what’s really going on when angelfish stay at the top and how you can fix it.
Low Oxygen (Most Common Reason)
Even if the water looks perfect, there might not be enough oxygen. Warm water holds less oxygen, and angelfish are fairly large fish — they breathe a lot. When oxygen drops, they naturally swim to the top where the water has the most air exchange.
You may also notice:
• Faster gill movement
• Hanging near the filter outlet
• Occasional gasping
Adding surface agitation (like moving the filter output higher) or using an air stone usually fixes this quickly. Clear water doesn’t always mean oxygen-rich water.
Ammonia or Nitrite — Invisible but Deadly
New tanks or uncycled filters often have ammonia or nitrite spikes that you can’t see. These chemicals irritate a fish’s gills, so they go to the top where breathing feels easier.
Signs include:
• Red or irritated gills
• Angelfish refusing food
• Staying still near the surface
Even a small spike can force angels upward. Testing the water is the fastest way to confirm this.
Temperature Too High
Warm water rises to the top, and so do fish when things get too hot. Angelfish prefer stable temperatures around 26°C. If your tank goes above that especially 30°C or more oxygen drops and stress increases. They stay near the surface to cool down and breathe easier.
Check your heater. Many hobbyists don’t realise the heater is malfunctioning until the fish react.
Filter Flow Too Strong or Too Weak
If the filter output is blasting the tank, angelfish avoid the bottom because the flow is too uncomfortable. Bettas usually get mentioned for flow issues, but angels don’t like strong currents either.
On the opposite side, if the filter is too weak or clogged, the water becomes still and oxygen drops — which again sends them to the top.
A gentle, steady flow is perfect for angelfish.
Stress From Tank Mates
A bullied angelfish will often hide at the top. It’s the safest place for them if the bottom or middle is filled with pushy fish.
Signs of this:
• Torn fins
• Other fish chasing it
• Staying in corners or behind equipment
Sometimes even another angelfish can be the problem — pairs and groups form hierarchies, and weaker angels often get pushed upward.
Parasites or Internal Illness
If only one angelfish is affected and the breathing looks heavy, it could be a gill parasite or infection. This doesn’t make the water cloudy, so it’s easy to miss.
Look for:
• Scratching on decorations
• Mucus around the gills
• Not eating
• Slow movement
Illness usually affects just one fish first, not the whole tank.
Final Thoughts
When an angelfish stays at the top, it’s not random behaviour. It’s trying to tell you something about the tank. Most of the time, the cause is simple — low oxygen, hidden ammonia, warm water, or stress. Once you correct the environment, angels usually return to their normal slow, graceful swimming.