Corals and other invertebrates use calcium from the seawater in which they live. While there is an inexhaustible supply of calcium in the ocean, in the marine aquarium, calcium and alkalinity are depleted quickly. To support the healthy, natural growth of corals, a balanced calcium supplementation is essential. The Tropic Marin Bio-Calcium ACTIF Liquid Refill pack consists of three different salt mixtures (A, B, C) that get dissolved in water to refill the three bottles of Tropic Marin Bio-Calcium ACTIF Liquid Refill Liquid. This saves packaging and transport.Do you have questions about this article ?