Reef Casa Bacteria Hotel BlockSupercharge Your Biofiltration Each block of Reef Casa Bacteria Hotel is the equivalent to 5lbs of surface area of live rock ! These make the perfect surface for growing beneficial denitrifying bacteria which helps reduce nutrients and maintenance. Use with any Reef Casa all in one aquarium or place them directly in your sump. Key Features For Tanks up to 25 Gallons Super porous material Inert and will not leach Po4 2,000 in2 of surface area per box