Phreeqc is a software that can be used to calculate hardness in water. There are many factors that can affect the hardness of water, including the type of minerals present, the pH, and the temperature. I am not sure if figure 3 is correct in the attachment. The reason I am unsure is because the variance of seawater hardness when adding NaHCO3 seems to be very high. I would like to know if there are any solutions to this problem.