Salts are an essential component of fresh water, as they are a source of calcium, magnesium, potassium, and other trace elements for fish and plants.
GH is the total amount of dissolved salts in the tank (chiefly carbonate, chloride, and sulphate salts). Salts are an essential component of fresh water, as they are a source of calcium, magnesium, potassium, and other trace elements for fish and plants. They also affect the osmoregulation process in fish (i.e., maintenance of the internal to external salt/water balance), and a dissolved salt content above or below the tolerance of a specific species can cause a great deal of stress. Thus, it is important to maintain GH at an appropriate level via the addition of specially formulated aquarium salts (not sodium chloride or regular table salt) to increase hardness, or by diluting very hard water with soft water or RO (reverse osmosis) water to decrease it.