Freshwater Issues
Fish Gasping at the Surface
Symptoms
- Fish hovering near the surface, mouths working rapidly
- Gills flared, rapid breathing, lethargy
- Sometimes multiple species affected at once
Likely causes
- Low dissolved oxygen — high temperature, poor surface agitation, or overstocking
- Ammonia or nitrite poisoning damaging gill tissue
- CO₂ injection overdose in planted tanks
- Sudden parameter swing after a large water change
Immediate steps to take
- Increase surface agitation immediately — add an airstone or angle the filter return up
- Test ammonia and nitrite; if either is detectable, do a 50% water change with dechlorinator
- If CO₂ is on, turn it off until breathing normalises
- Lower the tank temperature 1–2°C if it is above 26°C
Long-term prevention
- Always keep an airstone or strong surface ripple, especially in warm months
- Avoid overstocking — research adult sizes before buying
- Use a CO₂ drop checker and turn injection off an hour before lights out
- Test water weekly, not only when something looks wrong
Recommended products & practices
Oxygen is non-negotiable. A simple air pump and stone is the cheapest insurance in the hobby — every freshwater tank should have one available.