Thanx for the replies.
I have a 35G fish only set up.
Other fishes besides Gramma are 2 percs and a scooter blenny. Tank has been cycled and running for 5 weeks or so, water parameters are fine.
Other fish are not showing any symptoms.
I gave the Gramma a freshwater dip (bath?), and this morning it was not rubbing off rocks or sand.
I have purchased medication that says it treats most diseases, and doesn't harm invertibrates etc. I will keep a close eye on things.