Use the Pond – Hardness Test for testing the general hardness and carbonate hardness of your pond water. This test kit measures GH in dGH (where one degree = 17.8 ppm as CaCO3). For pond fish, between 8 and 12 dGH is ideal, GH looks at the total amount of dissolved mierals in the water. The kit also measures KH in dKH (where one dKH = 17.8 ppm as CaCO3). It is essential to maintain a minimum KH level of at least 4 dKH at all times. A KH of between 6 and 8 dKH is more desirable. KH is looking at the buffering capacity of the water and how well it can resist changes in pH.