The calcium hand-waving game

[rbarba]

I'm wondering if I can get some debunking help.

Our water-testing system here typically calls for the addition of outrageous amounts of calcium to pools when given a strip water sample. It's a glorified scanner with a color-picker in it where different shades on the strips correspond to ppm's.
Being that 99.9% of our customers have vinyl liners (that's what we install), I never recommend the addition of calcium. Why buy stuff you don't need, and then have to drain water because the system told you to add 19 pounds of calcium?
However, I was told that "The amount of calcium in the water determines how much chemicals the pool can hold successfully."

Total BS? I'm not sure how calcium could affect the capacity of water to hold chemicals. Smells like an attempt to sell unnecessary chemicals to me.

 

[JasonLion]

The only known differences between very low CH and "normal" CH in a vinyl liner pool is that very low calcium makes foaming slightly more likely and normal/high CH makes metal stains slightly more likely. The foaming effect is very small and almost never matters except in a spa. The metal staining effect involves interactions with sequestrant, which will bind to calcium, reducing the sequestrant available to bind to metals. Calcium levels have no impact on FC, CC, PH, TA, Borate, Salt, or CYA. There is also the non-chemistry issue that low CH can sometimes invalidate heater warranties, not that it makes any actual difference to the heater. And finally, low CH can reduce pool store revenue.

As always, high CH can be a problem for any pool.

 

[chem geek]

Is your strip-reading test system actually measuring Calcium Hardness anyway? It's probably measuring Total Hardness since most test strips don't test Calcium Hardness.

 

[rbarba]

Yes, actually it is total hardness. The scanner, though, just says that pad is calcium hardness. That's an issue.