Need more info: do you have a sump w/ macro algea? What kind of lights, nitrate & phos levels? Changing socks? How often? Tangs? CUC makeup/mix? That tank looks pretty “tidy”, is it too clean?
Anyway, before reaching for Vibrant, try “killing it softly” : 100 micron sock change 3x/week , rinse (or not rinse) your frozen... feed less, I’ve even Removed rocks and carefully dripped 3% peroxide on infected rocks.... I’m guessing Just by the looks of your tank you will be successful...
Edited to add: sometimes, and I mean sometimes, urchins do a better job of stripping down rocks to the bare surfaces...on the downside theY wreck a aquascape, eat coraline algae and thier sandy poop isn’t pretty, but they definetley eat suff other CUC species pass up