Jessica, welcome to RF!
Lime water is also known as Kalkwasser, which is a way to add calcium to your tank for all calciferous organisms. Snails, stoney corals, crabs, shrimp, and coraline algea are just some examples of organisims that preciptate calcium from the water column to build their skelatons and exoskelatons.
One must be very careful to drip the solution slowly as to not reate a chemical imbalance in your water column and spike your Ph too high. You need to test your Ph ans Alk to ensure they are in balance and your calcium stays in the 400 - 450 ppm range.