The total hardness of water generally represents the total concentration of dissolved calcium and magnesium ions. Although closely related to alkalinity and the buffering capacity of water, high alkalinity may not always indicate high hardness. Hard waters (above 150 ppm) are generally more productive
for fish than soft waters. The typical range for aquaculture is 50 to 200 ppm. Testing takes 2 minutes. 0 to 200 ppm.