Pet Petco Snowy River Aquarium Gravel, 5 lbs. Stone, Gemstone, Decoration, Design, Non-toxic, Pebble Supply Store/Shop Aids in propagation of beneficial bacteria Adds depth and beauty to aquariums, water gardens, ponds and terrariums Made of non-toxic fish safe materials and colors Safe for use in freshwater and marine environments For optimum results, use 2 lbs. of gravel per every one gallon of water