My experience with Blenny's is minimal so I don't feel I could offer any valid guidance there. Variety...
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I can empathize with your fear of a parsite and wanting to isolate however I'm of the belief that if you suspect a fish has been infested, it's obviously present in the system so the other fish have already been exposed to it. Their immunie system is just capable of dealing with it. Disturbing the tank trying to capture a few inhabitants will merely stress them all out, thus weakening their immunities. Besides, there's no indicators of a parasite. Not externally at least. As mentioned, these are merely my beliefs, some may disagree. It's difficult to determine when to treat, what are we treating, who get's treated etc. In a "perfect world" we wouldn't have to ponder those decisions...