Other than adding to the beauty of your aquarium, a proper aquarium substrate is crucial to providing a surface for beneficial bacteria to attach to. Our line of low cost Pure Water Pebbles are 100% Acrylic Coated Natural Gravel will not alter the chemistry of your aquarium water, is Non-toxic and Colorfast. As with any other aquarium substrate you might use, make sure you wash the gravel with plain water (no soap or cleaners!) before adding it to your aquarium.