Occasionally you may get more algae than your shrimp can eat or if your population of shrimp has reduced they may have trouble keeping up. These easy to use magnets are just what the doctor ordered. It is recommended that you use it as soon as you see evidence of algae build up on the walls of your system. It is easy to control if you stay ahead of it. We recommend moving it to an area with a little less light after cleaning. Given the right environment cleaning is not necessary.