If you only learn one thing about Epistylis, make it this: the visible symptom is rarely the real problem. The good news: most cases are treatable at home if you act in the first few days.
The symptom
Cotton-like clumps that do not wipe off easily, often on weakened fish.
What is actually causing it
Ranked by likelihood:
- Stress from poor water — ammonia or nitrite above 0 ppm, or nitrates over 40 ppm.
- Secondary infection — a wound or parasite opens the door.
- Temperature swing — more than 2 °C in a day weakens immunity.
Test the water first; treat the cause, not just the spot. A the led vs fluorescent aquarium lighting: what actually matters makes the numbers obvious.
The treatment
Step by step:
- Move the sick fish to a hospital tank if you can — see our cloudy eye and popeye: what the swollen eye means guide.
- Raise the temperature slowly to 30 °C to speed the pathogen's life cycle (species permitting).
- Add 0.1% aquarium salt, dissolved first, and keep it stable with a 25% water change every other day.
- Follow the medication label exactly; overdosing does more harm than the disease.
Prevention
Quarantine every new fish for 3 weeks, keep nitrates under 20 ppm, and avoid overcrowding. Stability is the best medicine — a tank that holds its parameters rarely sees outbreaks.
