Since openning my pool in early May, I have been experiencing huge FC losses daily. Water is crystal clear, however. My pool is 15K gallons, in-ground liner pool with cartidge filter. My numbers are good except for the FC loss. Ph- 7.4, CYA- 40-50, TA- 110. So I have held my pool at shock level or above for over 10 days now with no improvement. For example, last night at 8 pm I tested FC levels and they were at 18-19 ppm, which was a huge losss from the day before. So I added 8 gallons of 6% bleach and retested at about 11 PM. Fc was up to 42-43 ppm. This morning at 7 AM, FC was down to 37 or so, with no cc showing. At 10 AM this morning it was down around 28-29 ppm with cc .5<. I have been at this battle for too long, and it's getting expensive. My water looks crystal clear and inviting, but based on my testing, I am battling something. Oh yea, all my reagents were replaced with new ones because I thought they might be giving me bad results.
Any suggestions would be greatly appreciated. I am thinking a partial drain and re-fill might be the least expensive option, since continued shocking has not worked.