I'm puzzled by the steadily declining behavior of CH that I'm seeing as I startup our new pool. I'm testing with the the TF-100 kit, aiming for a neutral startup of new white plaster in 50K gal pool. It was plastered/filled Friday.
The fill water tested at pH 7.8, TA 100, and CH 200, with fill completed at 7:30pm. I added the sequestering agent that the plasterers provided, during the last of the fill. Builder's startup operation advised I do nothing else until our appt. the next morning.
At 7:30am Saturday, numbers were pH 8.2, TA 125, CH 185. The builders startup crew arrived at 9 am Saturday, installed the floor cleaning heads and other bits, and started the pumps. Over the course of the day, I added 3 gallons of muriatic acid, and brushed 3 times, resulting in 10pm numbers of pH 7.0 TA 70 CH 180. 8am Sunday, pH 7.2 TA 85 CH 170. 3 rounds of brushing, pH rising over the day, eventually at pH 7.8 TA 80 CH 140. Added 1 gallon acid, bringing pH down to 7.2.
I thought that the curing plaster would be contributing some dissolved calcium compounds to the pool water, so am puzzled that CH could go 200->185->180->140 as we brushed, filtered, and added acid.