Pool started in June 2009 (17.5k gal, SWG). CH was in the 300 - 350 range last year. Tested for CH today (for the first time this year) and have a reading of 400 from the pool store and 450 from the TF kit.
What causes the hardness to increase? Have only added acid and baking soda on a regular basis.
We do have naturally hard water, but with our cold winter I can't believe much fresh water went into the pool in the last 3 months (auto fill). Will CH continue to creep up after I drain 20% and refill?