Calcium Disappearing?

[spidey9]

Background: Jacuzzi J-345, 340 gal, using dichlor-bleach method, used daily for one 20 min soak by 1 or 2 people, all testing done with Taylor K-2006 except as noted.

My local water has a CH of about 100, and at my last fill (2 months ago) I added CaCl to bring that up to about 150.

I check chlorine and pH daily, and do a full set of tests weekly.

The last couple of weeks my CH has dropped off to nearly nothing, When I add the 5 drops of R-0011L the sample immediately turns mostly blue rather than red. I have repeated the test several times and checked my methodology by testing a 200 ppm sample reagent, which gave the expected results: the sample turned red with the R-0011L and turned blue at the 20th drop of R-0012.

Other readings are fine: pH 7.6, FC 2.8, CC 0.2, TA 65, CYA 32.

The only things that have been added to the water are dichlor, bleach, occasionally dry acid to knock ph back down, and Spazazz aromatherapy crystals, which consist primarily of magnesium sulfate.

Also, salt and TDS measured 400 and 600 respectively at the fill, and have gradually increased to 1800 and 2900, as measured with a SafeDip pool tester (which may or may not be accurate).

What could cause the calcium to disappear? Should I add CaCl to bring it back up, or not worry about it? The water looks and feels great.

[chem geek]

That's strange. The Calcium Hardness test does add a base to precipitate magnesium as magnesium hydroxide, but that shouldn't cause the test to read falsely low if it were overwhelmed with too much magnesium -- it would read too high if anything. So I don't know what would cause it to drop except for certain calcium removal products such as Hot Springs Vanishing Act.

You don't have to worry about the calcium unless you are seeing foaming. That's the main reason to have 120-150 ppm calcium in the water and I presume you have no calcium carbonate plaster/grout surfaces exposed to the water.