Carib Sea ACS00370 South Sea Base Rock for Aquarium, 40-Pound At an unprecedented 50% void space (macro and micro), you will be hard Pressed to find a durable natural Rock that has this magnitude of porosity Natural weathering processes form the fantastic shapes of South seas base Rock by the erosion and pitting of Limestone over the course of eons Safe for all marine and high ph freshwater systems Calcium Carbonate rock supports health ph Made in the USA