Unable to lower pH and total alkalinity

[garbz123]

I have a 40 x 20 gunite pool about 35,000 gallons with mineral springs bioguard salt system. The pH has been around 9.0 with total alkalinity around 230. I have been pouring in tons of dry acid daily and can not get the pH to stay down. It might lower momentarily put then goes right back to pH 9.0. Also the sand filter had been needed to be back washed more often than normal. ANy suggestions on how to resolve this problem would be greatly appreciated.

[chem geek]

You aren't using nearly enough acid, and you should be using Muriatic Acid so that you don't keep increasing your sulfate levels which eventually could harm stone coping and plaster surfaces. It takes 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons to lower the Total Alkalinity (TA) by 10 ppm. So it will take 3.5x that amount to lower the TA by 10 ppm in your pool. You'll need to add a LOT of acid, but the key to lowering TA is to also aerate the water at low pH. Follow the procedure in this post. Your pH will not rise as quickly when you get your TA lower.