Torn, ragged, or disappearing fins
This looks like: mechanical damage from aggression OR bacterial fin rot — sometimes both once bacteria move in
Why this happens
Sharp clean splits often mean aggression or décor. Black-edge melt with red spreading often rots. Poor water worsens every version.
What to do right now
- Test ammonia and nitrite — rot thrives in dirty margins.
- Rearrange or add visual breaks; watch after dark.
- Salt only if species tolerate — research first, measure grams.
- Dose appropriate antibacterial only if rot advances after water is clean.
- Never tear extra fin with net rush — slow net, calm handling.
What not to do
- Don’t leave long-finned fish with known nippers without exits.
Stop it happening again
Don't mix fin-nippers with long-finned fish, give everyone space and cover, and keep water clean so small tears don't turn into rot.
If that doesn’t fix it
If body ulcers appear, jump to bacterial ulcer path.
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.