Spectrastone Aquarium Gravel - is a high quality, polymer coated gravel ideal for aquariums, terrariums, crafts and planters. Because it is composed of inert stone, our gravel will not buffer PH and is suitable for fresh water environments. We now use an environmentally friendly plant based coating. For optimal decorative effect use 1.5 to 2 lbs. of gravel per gallon of aquarium capacity, or 180 to 240 grams of gravel per liter of aquarium capacity.