The black molly is a fish that a lot of people rarely think about when thinking about algae solutions. The truth is that mollies do in fact help with cleaning up the algae in your tank. They might not be as good as other fish, but they will add a little bit of help. All mollies will eat algae, but out of all of them, the true black molly (Poecilia Sphenops) is the best of the group. They will usually help with the algae growing on rocks and plants.