Since 1974 Peter Wilkens was aware that calcium was one of the principal elements in the saltwater mixture whose use therefore depleting in the aquaria, led to failure if it was not replaced. Peter Wilkens developed the method called Kalkwasser (a mix of calcium hydroxid with water, preference osmosed), which is easily assimilated by the animals and algae whose building needs calcium. ReefKalk, Calcium hydroxid allows the keeping the growth and the multiplication of the most difficult stony corals (sceractinia). ReefKalk makes possible the culture of different red calcareous algae, Corallinacea and green algae like Halimeda. To be used daily.