CNZ Mix Color Polished Natural River Pebble Stone, Grade A, 1.0-1.5", 10 lb. Aids in propagation of beneficial bacteria Adds depth and beauty to aquariums, water gardens, ponds and terrariums Made by nature river pebble stone, average size: 3-5Mm Safe for use in freshwater and marine environments For optimum results, use 2 lbs Of gravel per every one gallon of water