In case anyone out there has had problems getting a free chlorine reading in a sparkling clear pool, the problem may be high phosphates. Last year I battled most of the summer trying to get a free chlorine reading in my vinyl lined, inground swimming pool, (17000 gal). After speaking with my pool person, they ended calling their pool rep, and it was determined that I had extremely high phosphates. Upon their advice, I added Sea Klear phosphate remover, ran the filter for 48 hours, retested for phosphates, and found none. I did learn that phosphates consume and affect the chlorine reading in swimming pools. I also have no algae problems at all, with no phosphates in the water.
I do have a question, does adding CYA really aid in preventing the loss of chlorine. I just tested for CYA, and it read 10. Should I add CYA to get a reading between 40 and 80 I believe. (don't have my test results in front of me from my pool place). Also, is it better to shock with hypo cal, or the liquid chlorine (sodium hypochlorite?) My free chlorine reading was 1.5, and my total chlorine reading was 3.