For freshwater and saltwater fishes. Calcium is important in fish hatchery water supplies. High levels of alkalinity and hardness can lead to precipitation of calcium carbonate from the water. Aquatic animals can get calcium and magnesium both from the water and their food. It may be used to treat conditions caused by low calcium levels such as bone loss (osteoporosis), weak bones (osteomalacia/rickets), decreased activity of the parathyroid gland (hypoparathyroidism), and a certain muscle disease (latent tetany).