Fluffy white patches (cottony)
This looks like: secondary fungus on a wound OR bacterial columnaris — both need clean water first; meds differ
Why this happens
True fungus often lands on an injury after dirty water. Columnaris spreads faster, mouth “saddle,” fray edges — but photos overlap. Water quality first, identification second.
What to do right now
- Large partial change with conditioned water — improve environment before dosing.
- Take sharp photo with light angled across patch texture.
- Remove carbon if medicating per label.
- Separate worst fish if others pristine — easier to treat target.
- Research antibacterial vs antifungal — guessing wastes time.
What not to do
- Don’t mix five meds — lethal cocktails.
Stop it happening again
Keep water pristine and avoid injuries from sharp decor, rough netting or nippy tankmates - fungus and columnaris both target damaged, stressed fish.
If that doesn’t fix it
Mouth rot in cichlids — community forums often tag columnaris patterns.
Catch this earlier next time — log your water parameters in App-aquatic. Free forever.
This isn't veterinary advice - it's a directional read to help you decide your next step, based on the most common causes. We can't see your fish, so pair it with a liquid test kit and clear photos, and see an aquatic vet or a trusted local fish shop for a valuable or seriously ill fish.