My 18,000 galloon pool continues to have high PH even after I add PH Minus. It was at 8.3, I added 3lbs of PH minus as suggested and it went down to a little but a day later it's back up again,. The CYA is at 28,T TA is 110 and FC is 2.5, any suggestions on how to get the PH down and stay that way? Is being on the lower range of cya causing this?