Hardness Water Hardness is an indication of the calcium and magnesium content. If the water is very soft, less than 50 mg, you may need to provide supplemental calcium and magnesium. Potassium and Phosphate These essential plant macro-nutrients normally occur in very low concentrations in water. If the water contains more than a few ppm of these elements there is a possibility that your water may contain fertilizer, detergent or other contaminants. Potassium is involved in maintaining the water status of the plant and the tugor pressure of it's cells and the opening and closing of the stomata.
Potassium is required in the accumulation and translocation of carbohydrates.
Lack of potassium will reduce yield and quality. Older leaves will be scorched on edges. Plant will become susceptible to disease and toxicity. Excesses will interfere with magnesium and calcium availability. ATP is involved in various energy transfer reactions, and RNA and DNA are components of genetic information.