I have been wondering for awhile if I am using the Salifert test kit for Calcium correctly. The test kit instructions say to dose solution number 3 to the test vial until the solution turns "clear blue" (swirling the test vial after each drop). On a recent test I got a distinct change to what I would call purple at 350, what I would term purplish blue at about 370, and true blue at 400. The problem with color is that it is so subjective... I am hoping that I am reading it right and calling it 400. Any help?