Be careful with lawnmower blennies. They live up to their name and mow down your algae....problem is they are too good at their job and they can sometimes get so picky that they only will eat algae and essentially starve themselves
That's what happened with mine, except my problem was I have a low nutrient system with little to no algae. He wouldn't eat anything I tried to feed and of course died.
Bought a starry blenny and he is a complete pig, along with being one of the funniest critters in my DT