sera guide - Marine aquariums

42 These substances must be replenished regu- larly for maintaining natural conditions in a ma- rine aquarium, especially after a water change. This is the only way to ensure optimal, healthy growth of the animals. In particular corals, but also snails and clams withdraw calcium and trace elements from the water. Also, bacteria in the sediment can reduce these elements by precipitation. 9.3 Supplying trace elements, calcium and macro elements