Dave your blenny has a pot belly, there's plenty for him to eat. lol.
I'm not sure what he's eating, he picks at the rocks only, I have not seen him eat off the glass like the others did. my rocks have a few patches of hair algae, he does not seem to touch those.
Mike depending on the size of the tank you could also try some yellow tangs, even one will make a difference. I also got one from Dave and it's been eating everything off the rocks as well. The only problem with tangs is they poop a lot which can raise po4, and no3, I actually have nitrates reading for the first time in my tank,about 1.0
I attribute this to the fish I have added that Dave gave me, algae blenny, yellow tang, and hippo tang. You might want to increase the water changes for a while and see if that makes a difference. make sure the RO water you use is at least 1 TDS otherwise it may not make a difference. Also a bigger skimmer may help. I'm going to have to add a larger one now that I'm seeing nitrates in the water.