Anti-scaling and calcium test

[CaOCl2]

Would the use of an anti-scaling product in spa water interfere with the calcium test? I'm getting a very very pale red, almost invisible, then a very very pale blue endpoint, almost clear.

I tried the usual adding of a few drops of titrant before the titration and no change.

I also tried adding a few grains of CaCl to the sample in the hopes of getting some real color happening, but no go.

 

[Guest]

What are the indgredients in the anti-scaling product? Many of them contain a seqesterant to seqester the calcium so they would lower the calcium reading that you get on the test. Some of them tend to lower the pH of the water to dissolve the scale. If the pH is very low it could have an impact on the test.

 

[CaOCl2]

What are the indgredients in the anti-scaling product? Many of them contain a seqesterant to seqester the calcium so they would lower the calcium reading that you get on the test. Some of them tend to lower the pH of the water to dissolve the scale. If the pH is very low it could have an impact on the test.

It's "Spa Essentials Stain and Scale Control II", I do think this is it right here: http://www.bel-aqua.com/msds/omni/423450.pdf

Basically HEDP at 27% and phosphorous acid at 1%. Would that "bleach out" the R11L?

The pH checked in at 7.1 yesterday, alk at 90 (curiously the sample turned blue-ish instead of green but the endpoint was bright red). About 6 ppm bromine.

I've tested the water for iron and copper and both show 0 ppm.

Unfortunately there's about 120 km between me and that water source and I have about 30 ml of the sample left . . .