how much dry acid sulfite problem

[central nj]

Hi,
I have about 30lbs of dry acid left from last year (new pool plaster). I'm now comfortable using muriatic acid btw----but i have all this left over dry acid. My pool is still needing 12 oz of muriatic acid a day. I realize dry acid adds sulfites, which apparently damages the pool. But how much of the left over acid can i safely use, before switching back to liquid?
Thanks

 

[chem geek]

Based on this thread, the limit of sulfates to prevent concrete/plaster problems is around 300 mg/L (ppm). If you are starting with near zero, then in your 16,000 gallon pool you'd get 300 ppm sulfate after adding cumulatively 800 ounces weight (50 pounds) of dry acid (93.2% sodium bisulfate). And that assumes no water dilution.

 

[central nj]

Mr. ChemGeek--thanks. Is it unusual at 11 months after replaster to still use so much acid? I was forced to acid wash due to scale 4 weeks ago (my numbers got out of hand last year after the replaster). Could the acid wash refreshening be contributing?

I'm using about 12 oz muriatic a day, usually one "acid demand" drop worth from the taylor kit--about 0.2 rise in ph a day.


TA 110
CH 170
CYA 25
Borates 50
PH 7.4-7.8
FC 2-5
CC always 0


Thank you to this forum!!!!!!!!!!!!!!!!!!!111

 

[chem geek]

Try lowering your TA to 70 ppm and see if that helps. If it does, then raise your CH level since it's on the low side and you should have more if you're going to have a lower TA. Also, don't lower the pH below 7.5 and let it get to 7.8 before you add acid.