Cladophora aegagropila is an aquatic moss that is slowly formed into a ball over a long period of time. Originating in very cold rivers and lakes throughout Northern Europe and Japan these Marimo Balls or Moss Balls as they are more commonly take long periods of time to form. Cladophora aegagropila will not cause algae to form in your tank. In fact, Marimo Balls will do the opposite by taking nutrients out of the water. Moss Balls are a different type of algae than those that normally form in an aquarium and are very slow growing. ~1" diameter.