Likely cause
Fin Rot
Ragged, frayed, or disappearing fin edges — sometimes with a white or red tinge — usually point to fin rot, a bacterial infection that takes hold when water quality is poor or a fish is stressed. Improving water quality alongside treatment gives the best results.
Why this happens
- Poor water quality — elevated ammonia, nitrite, or nitrate — is the most common trigger, since it stresses fish and lets opportunistic bacteria take hold.
- Physical injury from aggressive tankmates, sharp decor, or fin-nipping species can create an entry point for infection.
- Overcrowding and low oxygen add ongoing stress that makes fish more susceptible.
What to do next
- Test your water and do a partial water change to correct any ammonia, nitrite, or nitrate issue.
- Treat with a fin rot / bacterial medication.
- Remove or separate any aggressive tankmates that may be causing physical damage.
- Keep up regular water changes during treatment — clean water speeds recovery and prevents reinfection.
Frequently asked questions
Will fin rot fins grow back?
Yes, in most cases — once the infection is treated and water quality is stable, fins regrow over several weeks, though the edge may look slightly different than before.
Can fin rot kill a fish?
Left untreated, it can progress to the fish's body and become fatal, so it's worth treating as soon as you notice ragged or receding fin edges.