General Hardness (GH) Test Kit

The General Hardness Test Kit uses a drop-count EDTA titration method where each drop of reagent consumed corresponds to 1 dGH (17.9 ppm CaCO3). GH measures the total concentration of dissolved calcium and magnesium ions, which are critical for osmoregulation in fish, shell formation in invertebrates, and nutrient uptake in aquatic plants.

The test involves adding drops of reagent to a 5ml water sample until the colour changes from orange to green, with the number of drops equalling the GH reading. The method is inherently precise and free from the colour-matching subjectivity of comparator-based tests.

GH is a stable parameter that changes slowly but should be tested when setting up new tanks, mixing RO water with tap water, or troubleshooting plant deficiencies and shrimp moulting problems. Freshwater fish span a wide GH preference from 1 dGH for wild discus to over 20 dGH for hard-water cichlids.