Invertebrates
Popular algae eaters are e.g. the sea urchin (Mespilia globulus), which is also suitable for smaller pools from about 100l, or sea urchins from the relationship of Tripneustes ssp.. Starfish feeds mainly on growth such as bacterial deposits and therefore need a mature, large aquarium (from 300l), which should not be too sterile.
A peculiarity are sand-digging sea urchins and starfish such as the sand dollar or the sand-digging starfish, which circulate the ground and rid of dirt and algae. When inserting into the pool, sea urchins and starfish should be under water at any time.