Tropic Marin Pro-Coral KalkOur Tropic Marin Pro-Coral Kalk is calcium hydroxide in its purest form and is used to make up the classic limewater advocated by Wilkens. Pro-Coral Kalk increases pH and calcium content to promote the growth of corals and calcareous coralline algae. It inhibits the growth of undesirable algae by binding carbonic acid, one of the inevitable by-products of operating a CO2 calcium reactor.