Sera KH-plus 250 ml water conditioner is used for safely increasing the carbonate hardness (KH) in fresh and salt water. 5 ml of sera kH-plus increases the carbonate hardness in 40 litres aquarium water by 1 dKH. The carbonate hardness in freshwater community aquariums should be 5 - 10 dKH, in saltwater aquariums 8 - 12 dkH. First check the carbonate hardness by means of a kH-test. Then add sera kH-plus directly into the aquarium. It's recommended that you increase the carbonate hardness by a maximum of 2 dKH per day.