redlessi

It almost looks like the tail is getting ready to come off, the fuzzy spot is right where the tail meets the body. Water params 0, 0, 10 with weekly water changes, this is in the 35 gal. I removed it from the tank and now I am wondering if my other fish will get it.

AlyeskaGirl

Hmmmm.....fin nipping could cause that, possibly your Danios doing it because they can be nippy. Just an idea since your water readings are good. Doing some daily water changes to keep the water clean with Stress Coat will help your Otto. Did you put him in a q-tine tank? I hope it all works out. Your other fish should be ok since you removed him, just keep an eye on them and keep up on your water changes. Keep an eye on your Danios to see what they are up too.