LifeRock Large Arches add open dimension to large marine and reef aquariums with plenty of swim space and area for coral placement. Each Plateau is 18 inches long and weighs approximately 20 pounds. One arch per box *please do note dimensions and weights varies as these are hand-made products. Life Rock is real aragonitic base rock, not cement, no curing. Extensive macro and micro-porosity infused with spored bacteria for outstanding biological performance. Clean and safe for all fish and inverts, environmentally responsible each piece being very unique.