I would get some snails.Turbo and nerites are good algae eaters.
The tank is too small for any algae eating fish and I'm all against hermit crabs(they are a pest and will bother/eat stuff you don't want them too).
Some urchins will eat algae also and look pretty cool.
Your best solution for algae is lighting control and good water quality,as too much light and nutrients like nitrates will encourage algae growth.Without corals that need light you could run lights only while you are watching the tank.
Oh and another source of algae is improper spectrum of lighting.Most marine tanks run lights from 10,000-20,000K.
Enjoy!
The Best Saltwater Snails for Algae Removal | Animals - PawNation