Black aquarium gravel for freshwater aquariums. Will not affect PH. Safe for use in freshwater aquariums. Aquarium Gravel and Color Coated Aquarium Gravel for: your aquariums, ponds, gardens and architectural surfaces. Heat sanitized, hand washed, safe for your fish, and ready to be added to your aquarium. These all-natural types of gravel are a great alternative to using artificial plastic or rubber ornaments. Pure Water Pebbles aquarium gravel helps to bring out the colors in your fish and the tank back ground. Safe for use in freshwater aquariums, will not alter the chemistry of your aquarium water.