I am wondering why my PH drops fast. I test my pool weekly. All numbers are fine but my PH which drops every week to 7.0 or below, so I add the amount of borax needed per the pool calculator but it still drops back to 7.0 the following week. I didn't have that problem last year. My FC is 5 and my CC is 0 to 0.5, TA is 70 and CYA is 75.