Stone keeps water fresh and healthy long and long time by absorbing all the wast Each stone is unique, precisely Hand-picked, Washed and Inspected It works as a good biological filter because most of the healthy bacteria grow between them or work as a great part in decoration Best Rocks for Garden Decor, Aquarium Decor. Some Rocks Works grate in Reef tanks and Others in Planted Aquariums Gives more attraction to a live planted aquarium