Okay - it happened again. Added the pool math recommended amount of Muriatic Acid to get it down to 7.2 from 8.1 and it only went to 7.5. Also, did an overnight test on my SWCG. Pool math says based on run time, run % and output of my cell I should have seen a 2.8 ppm gain in FC over the 8.5 hours I ran it. I experienced a 1.5 ppm gain. Any advice is appreciated. I realize I need to shock the pool, not sure if I should SLAM. Pool is crystal clear. Here are my levels:
FC: 6.73
TC: 7.12
pH: 7.5
TA: 62
Hardness: 518
CYA: 67
Phosphates 164
Salt: 3500