Yeah, I did the same thing as you. I've had blennies before and never had any issues with them. So I didn't think twice when I took one home.

The bare spots started showing up 48 hrs after I got it. At first I thought it was some kind of rtn event, then I saw the little bugger munching on just about every acro I had. After I removed him all the missing tissue on the sps healed over after a couple of weeks. Get him out as fast as you can.