Health guide, not a diagnosis · Serious
Low oxygen
Also called hypoxia, oxygen shortage
Signs
- Many fish gasping at the surface at once
- Fish crowding near the filter outflow
- Worse at night or in hot weather
Cause
Not enough dissolved oxygen: hot water, weak surface movement, overstocking, or rotting food or plants.
What to do
Add an air stone or point the filter outlet at the surface now, do a cool partial water change and remove any dead fish or rotting food.
If a fish is badly ill, talk to an aquatic vet.
Prevention
Good surface movement, fewer fish, cooler water in summer.
Species often affected
0 species