Diamond gobies are the best sand sifter in my opinion but they don't always eat the algae, if it's a lot, they'll ignore that area of the sand.
Anyways, what type of algae, is it algae, diatoms(brown) or cyano (red/reddish purple)?
Things to keep your sand clean:
Sand sifting gobies
Sand sifting starfish
Nassarius snails will sift sand and help keep it clean but they DO NOT eat algae, they are meat eaters.
Cerith Snails - great for diatoms and other algaes
Conches
Hermits (eat very little and usually climb on the rocks, but they will clean the sand as well)