The CaribSea Life Rock Arches consists of real aragonitic base rock, not cement. Requires no curing. These arches have extensive macro and micro-porosity infused with spored bacteria for outstanding biological performance. No curing required, clean and safe for all fish and inverts. Environmentally responsible and each piece is unique. Infused with beneficial bacteria 20 lbs box contains 4 rocks approximately 12" long each Safe for reef or hard water aquaria Each rock is unique and is a natural product