[mike31154]

What kind of Blenny? A Lawnmower? If so, I've had 3 of them in the past & each one had somewhat different feeding habits. One ate everything, including flakes etc. that was meant for my other livestock. But mostly they all mowed on everything in the tank that didn't move or sting, including the glass. Keep an eye on his belly area, if he's getting enough food, it will get quite plump.

Oh yeah, almost forgot! I doubt that hermit crabs are much in the way of competition for any Blenny, unless your system is crawling with them. The hermies I have are quite tiny & like most any crab, they're opportunistic omnivores & will eat almost anything, including scraps of meaty foods & of course each other sometimes.