API GH & KH Freshwater Test Kit.Tests tap water and freshwater aquariums for general hardness (GH) and carbonate hardness (KH). Helps detect stress on fish caused by rapid pH shifts, which result from low KH levels and helps aquarists duplicate the natural habitat of their fish. API GH & KH Freshwater Test Kit.Tests tap water and freshwater aquariums for general hardness (GH) and carbonate hardness (KH). Helps detect stress on fish caused by rapid pH shifts, which result from low KH levels and helps aquarists duplicate the natural habitat of their fish. Product code: 2430Item No. TK-API01058