Red Sea Magnesium Test: Chemical reactions?

[PotatoPig]

Does anyone happen to know the actual chemical reactions that go into the Red Sea magnesium test?

/Question is from one of my kids wondering how it works.

My guess is some sort of ph litmus test that has a rapid change that calibrates to the amount of magnesium on one side of of the equation vs the other. But that’s purely a guess.

 

[Randy Holmes-Farley]

Most magnesium tests work basically like this:

A dye binds magnesium and is colored.

A better magnesium binder (such as EDTA) is added slowly, and it is uncolored (or different colored).

When the color is gone, then you know how much magnesium there was based on how much of the stronger binder needed to be added.

The kit needs to distinguish calcium from magnesium, which can be tricky. One way is to add a binder that only binds and holds calcium away from the dye.