Blennies are really, really cool creatures. If you can find one that will readily accept prepared foods, then great! I had one in my 29 gallon and even though it constantly ate brine shrimp, hair algae, and film algae on my rocks, that still wasnt enough for it, and it starved to death. I couldn't get it to eat anything else. In a 180 gallon that is well established (atleast a year old) and has a LOT of algae, I'd say you might be okay, but having one accept prepared foods such as seaweed strips or nori would be a huge plus.