Adding Ph Increaser (and Ph Decreaser)

[sambo]

I need to know how much pH increaser is needed to raise the pH of a pool (of known volume) to a certain value. (Assume that the pH of the pool is a variable x and the volume is a variable y).

The pH increaser I am using (soda ash) has a pH value of 11 at a concentration of 1% solution in water.

I am trying to calculate the specific weight of soda ash needed to raise the pH but i am getting stuck on the calculations. If I get this answer I will be able to figure out the same for the pH decreaser (sodium bisulfate with a pH value of 2 at a concentration of 1% solution in water). Please help!!!

Thanks

[chem geek]

You can use The Pool Calculator for a rough calculation, but the accurate calculation especially when away from the normal conditions (pH 7.5, TA 100) is much harder to calculate. My pool equations spreadsheet here will do the accurate calculations, but the spreadsheet was not designed for casual users, but you might find it OK to use. If you have questions about it, you can just ask me. If your pool water chemistry test kit has an acid or base demand test, then that can be used to determine how much acid or base to add, but these demand tests have a rather low resolution since they seem designed for large moves in pH and not for smaller adjustments (since one drop of the reagent results in a somewhat large change in pH of 0.1 or 0.2 so it's hard to determine precise amounts of acid or base to add for smaller adjustments).

Basically, it takes more acid or base to move the pH when the TA is higher than when it is lower. Also, it takes more acid to move the pH lower when the pH is already low -- essentially the pH buffer resists change more at the lower pH.

Richard