Possible fin rot in royal gramma?

[flananuts]

I was finally able to get these photos while feeding. Tank is relatively new still, about 3 weeks old but stocked by TB saltwater.
I noticed yesterday two small areas on the edge of my gramma' tail looked at first to have some damage. Tank params have been pretty good however up until last weekend phosphates were 1 ppm based on an ELOS test. Nitrates have been around 5-10 ppm. I added phosban and did a 10 gallon change on a 43gal tank as well vacuumed the sump out. Phosphate is no longer detectable by test. I know I have some nuisance crabs in the tank that I have yet to catch, originally thought maybe a crab snapped the fish.

Fish eats well, feeding LRD Reef frenzy every other day. Images attached, would appreciate thoughts and recommendation on treatment sans QT. I don't think I could catch this fish even if I wanted to. If fin rot what do you recommend for treatment? Thanks.

 

[flananuts]

BUMP for a little fishy help

 

[liverock]

I don't see any issues....

 

[Deinonych]

If you're referring to the white spot on its tail, it might be lymphocystis. Lymphocystis is usually self-limiting and will resolve after a week or so.

 

[flananuts]

Thanks both. The fish is super active and eats well. Tough issue with an iPhone and a moving fish to capture. I'll continue to keep an eye on it.