The carbonate hardness (KH) is one of the most important water parameters in an aquarium. A majority of the fish species kept in freshwater aquariums prefer relatively hard water. Furthermore, the KH serves as a buffer that prevents dangerous pH value variations (among others, rapidly sinking pH value). The KH should be kept at least at 6°dKH for all community tanks as a basic rule (considerably higher for special cases such as African cichlids). This ensures the fish do well, and the aquarium water turns out particularly durable and easy to maintain. sera KH/pH-Plus precisely and lastingly raises the KH to the desired value. The pH value is gently raised as well and, above all, safely stabilized.