Causes for calcium leaving water?

[shore_pk]

I tested my source water that I use to (re)fill the hot tub for ch. It tests 170. On more than one occasion, about 5 to 6 weeks after refilling the hot tub the ch tests so low that I can't test for it.
I didn't know that calcium could be lowered in the water without draining and refilling with water that had less. Where does my calcium go?

With new water in the tub I have virtually no foam but by the time the ch tests so low I have a moderate amount of foam.

Linda

 

[PoolGuyNJ]

Is the water still warm or hot when testing?

Are you using strips to test for calcium?

What are the other chem readings and how are you testing?

Scott
PoolGuyNJ

 

[chem geek]

That is very odd. By any chance are you using a phosphate buffer for pH control? These are sometimes found in "one product does everything" miracles, that aren't. Phosphates will precipitate calcium out of the water.