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.