CaribSea Rock Lock Aquarium Cement (500 g) – A fast-setting, aquarium-safe cement for securing rocks, corals, and ornaments underwater. This specialized cement powder mixes into a malleable putty that hardens within minutes, allowing aquarists to build stable rock structures and prevent shifting in elaborate aquascapes. Rock Lock cement cures to a natural rock color and is reef-safe (contains no heavy metals or toxins), making it ideal for anchoring coral frags or fixing unstable stones in both freshwater and saltwater environments.