Gravel Grain Size 3.1 - 6.3 mm Premium freshwater aquarium substrate Natural gravel with 100% acrylic coating Non-toxic, colorfast, will not alter water chemistry Pure Water Pebbles are recommended for aquariums, ponds, terrariums, gardens, potted plants, vases, ash trays, crafts and hobbies, architectural surfaces, landscaping designs, and more! Be sure to check out all of the colors available to find the perfect gravel for your needs.