Measuring sodium tetraborate (borax)

[PoolDoc]

Unfortunately, Chemtura (BioGuard, AquaChem, many other brands) and especially Arch (HTH, other brands) have begun using magnesium sulfate to 'dilute' their calcium hypochlorite products. I think they may be using it elsewhere, too.

Regarding rain water -- I don't know if distilled water (rain water) could dissolve significant amounts of calcium and magnesium in the manner you imply. I'm guessing not, since roofing doesn't fail by losing all its grit. But you could check by testing the water you collect.

[Rebecca]

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

[waterbear]

If yo had no calcium hardness present the color would not turn red when adding the indicator. It would stay blue. It just means you have not added enough titrant to reach endpoint.
My suggestion is use a 10 ml water sample, add 10 drps of calcium buffer R-0010, 3 drops of calcon indicator R-0011 and then every drop of EDTA titrant R-1012 would equal 25 ppm calcium hardness instead of 10 ppm. Therefore every 4 drops is 100 ppm so the test will go much faster, particularly when calcium levels are very high.