Good thoughts on the improbability of dissolving magnesium.

I have been completely flummoxed about actual calcium hardness in my pool. The old total hardness kit used to give me a reading of 200-250. Per your advice, I switched to the Taylor 3 bottle approach, measuring only calcium hardness. It definitely turns red after adding 20 drops of #10 and 5 drops of #llL. So there is some calcium hardness present but I am not able to discern any change in color after adding #12. At first, I thought maybe there was a very very subtle shift in color to lavender but now I've done this test a lot of times and feel very uncertain....

To make this more complicated, the old total hardness test is not showing any hardness so I assume the chemicals have gone kaput.

Thank you, Rebecca