TA 120 to 150 over 2 days of rain

[adamjn]

Hello guys and gals - I have a question that has got me stumped.

At the beginning of this week, Monday the 4th, I began lowering my TA in preparation for the warmer weather to hit AZ very soon. Based on the pool calculator, I am aiming for 90-100ppm to keep my CSI at a decent level.

On Monday my TA was 130; I added 4 cups of acid per the calculator to starting bring pH from 7.8 to about 7.0-7.2. All was well the following day.
TA went from 130 to 120, pH to 7.2.

By Thursday pH only went up to 7.4-7.5 and TA held at 120. Then the rain hit - it added about 1.5-2" into my pool. pH shot up to 7.8 and TA went up to 130 again. By Sat most of the rain was gone, lite drizzle, so I added another 4 cups acid based on the calculator to bring the pH down again.

I check this morning, and my pH is at 7.2, right where it should be, but my TA shot up to 150...not sure how. I redid the test 2 more times...same 150 reading.

Overall results today are as follows.
pH 7.2
FC 4.6
CC 0.2
TA 150
CH 375
CYA 30

I'm at a lose here - does rain cause a rise in TA? Would acid rain have something to do with that?

The night before my readings were as follows.

FC 4.8
CC 0.4
pH 7.6
TA 130
CH 375
CYA 30

Any thoughts? I'm stumped at how 2 days of rain could bring my TA back up from 120 to 150. It seems i'm going to have to start the lowering processes over again.

 

[rjward]

Have you collected any rainwater and tested its TA & pH?

 

[adamjn]

Have you collected any rainwater and tested its TA & pH?

I have not. It didn't even cross my mind and I was under the impression that rain water wouldn't affect the TA like it did. In hindsight though, I will do this next time. From what I can see on weather.com, the rain is not coming back any time soon.

 

[JasonLion]

Remember that the TA test is +-10, so the change might not be as large as it appears to be. Of course it is also possible that the rain raised TA that much, though that is rare.

 

[adamjn]

Remember that the TA test is +-10, so the change might not be as large as it appears to be. Of course it is also possible that the rain raised TA that much, though that is rare.

Ah, I wasn't aware of the +-10. The thought also occurred to me that my sample bottle might need a good cleaning. I think I'll rinse it out well with some distilled water and then recheck later today when I get done brushing/vacuuming the pool down. It just seemed so strange to jump that much - I can't imagine the rain being THAT acidic/polluted where I am living.