I'm having a problem with high CH levels and I'm wondering what causes it to rise over time. The level was at 250 ppm in early January, 2011 and then started rising in mid-March. Between April, 2011 and June, 2012 it rose from 270 ppm to 575 ppm. It's now up to 675 ppm and I'm in the process today of draining and replacing a large portion of the pool water. The CH of my fill water is 160 ppm.
So, my question is, how can I prevent this from happening in the future? I've been using the BBB method (without any Borax yet) and the Pool Calculator set to TFP Goals since the pool was first filled after re-plastering in September, 2010. Could the curing plaster have contributed to the increasing CH levels? We are running an SWCG but I need to add bleach in the winter months when the water temp drops.
Here are the results from the latest test (Using Taylor Complete FAS-DPD test kit from Leslie's)
Pool Volume - 26,200 gal.
FC - 3.5
PH - 7.5
TA - 60
CH - 675
CYA - 60
Salt - 3800
Temp - 50f
Any help or advice appreciated.