As mentioned, they may eat some algae but only if they can't find anything else to eat. They are primarily scavengers that hunt leftover food. As for your algae problem, you need to discern what type algae it is first and then try to fix the problem. If it is something like blue green algae (not really an algae but a bacteria), there aren't any fish that will eat it. Other algae eaters such as plecos, otos, siamese algae eaters and amano shrimp will eat certain types of algae but not all types. So if you don't know what type algae you have, it's a shot in the dark as to whether the fish/shrimp you buy will eat it.