CaribSea LifeRock Arch (Large 18″) – A single large arched rock structure from CaribSea’s LifeRock collection, designed to be an impressive centerpiece in marine aquariums. This ready-made arch has natural-looking curves and openings, perfect for forming swim-through caves and coral display areas. It arrives in a rich purple “aged” color and comes infused with dormant beneficial bacteria to help kickstart the tank’s bio-filter. The LifeRock Arch allows aquarists to effortlessly create a stable, eye-catching reefscape that is free of nuisance pests and immediately visually appealing.