Lime water, a quicklime-water solution, is added to seawater aquariums to increase the calcium and alkalinity in the water. The calcium-rich lime water replaces the calcium used by sea creatures, such as coral, mollusks and crustaceans, to form their exoskeletons.
Another term for lime water is kalkwasser. This additive is essential, along with regular alkalinity and pH balancing, for a healthy saltwater aquarium. Lime water provides support to all aquarium residents with calcium carbonate skeletal systems. According to the Advanced Aquarist Magazine, lime water depletes necessary magnesium and strontium in reef aquariums over time. Both need to be supplemented when lime water is the primary source of aquarium calcium.