WARNING: I intend to retire June 1, 2019. This site will be go down at that time. Of course there is always the possibility of something happening before then, but you have now been warned.
Programs of this type are only as good as your environment measurements [ph, temp, ionic, purity] and the constants that you use. There is disagreement on what makes the best constants. Use with caution. Use the program that gives you the best results, even if it is not this one. See Other Programs for other programs hosted or linked to from here.