So Im not sure whats going on with my yellow tang. His fins have slowly been receeding over the last few months. At first I thought it might have been another fish bullying him around, but I never really see agression, except for a rare time him and the purple tang chase each other, but that does not happen often. But now it looks like fin rot, and Im not sure the cause. He is eating well (nori, pellets, & frozen) is fat, and is still very active.
My phosphates are at 0, and nitrates less than 5. Any idea what could be going on here?

Thanks!
My phosphates are at 0, and nitrates less than 5. Any idea what could be going on here?

Thanks!