Oh boy, this is my nightmare and I thought I had it at one point, long story short I didn't, but I had ruby reef on hand weeks before I noticed dots and tail biting on my blenny (again, it was sand and a nervous tick he does when others eat "his" food. And I dosed the tank making it look like a toxic spill.
I've heard good things about hydrogen peroxide, and now I dose it as a preventive and dino killer, but it might be too late for a management approach for you.
I wonder if anyone has had experience letting the tank cool down to make the fish slower and easier to catch? Or would that just hasten their demise?