The Salifert test kits for Ca, Mg, KH/Alk, and Phosphate instruct
Add dropwise with the 1ml syringe the <reagent> to the water in the test tube. Swirl after each drop a second or two. Continue with this until the color changes from <X> to <Y>.
It is not the case that all drops will be ineffective until suddenly one drop changes the color of all of the water in the test tube. Rather, you'll add drop after drop and suddenly you'll notice that one drop changes the color of a little
of the water in the test tube. As you continue to add drops, more water changes color.
My question is, am I supposed to take the reading the first time I notice a drop of reagent changing the color of the water in the test tube, once half the water in the test tube changes color, or should I keep adding reagent until all
of the water in the test tube has changed color and then take the reading?