Too much acid?

[zz28zz]

I have a 21,000 gal plaster in ground pool. My alkalinity (TA) was at 325 when I moved in 2 weeks ago. pH was 8.4... The guys at the local pool store did the water sample test and recommended 3 gals of acid. I've been taking them water samples every 3-4 days. Every time I get water tested the TA never drops as much as expected and I'm told I need more acid. As of yesterday, I've added 8 gals of acid (adding 1 gal every 2-3 days) and my TA is still at 180 (pH is 7.8 ). I run the pump a minimum of 3 hrs (with 2 water falls and 4 squirters going) after adding acid (usually at night) and the pump normally runs 8 hrs a day from 10AM-6PM.
I added my 9th gallon last night.
Whats going on here? This seems like an excessive amount of acid.
Could there be something else present in the water (that normally doesn't get tested for) that requires 3+ times more acid that it should need?

[chem geek]

In a 21,000 gallon pool, it takes 6.7 cups of full strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the TA by 10 ppm at the same pH before and after (i.e. you aerate as well as adding acid). So to go from 325 to 180 ppm would be expected to take about 6 gallons of acid. So 8 gallons is more than expected, but not 3x more.

The process goes faster if you add acid and aerate with the pH low as per the procedure described in this post. However, it sounds like you are well on your way.

[Guest]

Hmmm...

this alkanility is something quite new for me and could explain why I have to add so much darn acid all the time

I'll try to have the total alkanility measured and see what's up

JJ