• Spectrastone aquarium gravel is a popular substrate for freshwater and marine environments. Spectrastone will not change PH and is non-toxic and durable. For best results, use 1.5 – 2 pounds per gallon of tank capacity. We recommend rinsing the gravel prior to placing in your aquarium to remove any dust or fines. Use a water conditioner to remove chlorine and allow the water and temperature to stabilize for 48 hours prior to adding fish. by Estes, a privately owned company that has been supplying substrates to the pet industry for over 65 years!