macro algae hungry fish for 40 gal. cube?

[rickwaines]

Any suggestions for fish that would be at home in a 40 gallon cube. approx dimensions are 20 19 19. Currently I have a relatively new set up with a few soft corals: Clove Polyp and Dendros. A whole lota live rock, and some great macro algaes. Most of the algae are slow enough growing that I am able to control by hand but I would love a fish that loves Ulva algae. I look forward to your thoughts.

Appreciatively yours, Rick