Pure Water Pebbles Premium Fresh Water Substrates: Rainbow Gems Characteristics of Pure Water Pebbles Premium Fresh Water Substrates: Natural Gravel. 100% Acrylic Coating. Will not alter the chemistry of your aquarium water. Non-toxic. Colorfast. Recommended Uses: Fresh & Saltwater Aquariums. Ponds. Terrariums. Gardens. Potted Plants. Vases. Ash Trays. Crafts & Hobbies.