Topic split. Please ask questions in your own topic, rather than hijacking someone else's existing topic. JasonLion
I'm having trouble understanding how to calculate the amount of acid required. In my 300 gal. spa the starting TA is 200 and ph is at least 8.0. Your numbers from this thread suggest I need to add ~ 11 oz. acid (you don't specify what type, concentration, or whether by volume or weight). However, I can't duplicate that result using the pool calculator or the guidance that came with my acid demand test kit. Both of those suggest far less acid; plugging 350 gal, 200 starting TA, 60 goal TA, 8.0 starting ph, goal 6.8 ph into the calculator I see 3.9 oz 31.45% muriatic or 5.3 oz. by weight dry acid. I've tried the pool calculator recommended amount and sure enough, the ph barely moves even when not aerating, so I presume the numbers in this thread are more like it. Where am I going wrong in my understanding or operation of the calculator? Why don't the pool calculator numbers agree with your recommendations in this thread?