Lowered pH, TA stayed high

[tlhwxman]

Hello Gang,

Been awhile since I posted to the forum. I moved from Florida to Las Vegas this year . Got a new house with a nice big pool. I just had said pool drained and scrubbed (been sitting a long time). I refilled with city water.

Here is the problem. My TA is a bit high (120) coming from city water. I went to lower pH from 7.8 to 7.2 with Muratic (31%). The TA did not drop at all (still at 120). This doesn't seem right.

Here are few details

City Fill water: FC:0.0, CYA:0, TA:120, CH:220, pH:7.8, Temp: 68
Pool Water (now): FC: 11.5, CYA:40, TA:120, CH:220, pH:7.2, Temp: 69

I overshot on FC, so ignore that (my bad). I used 10% bleach to get it there. I added CYA and bleach at the same time I was dropping the pH. Could this be a factor why the TA didn't drop? Could the addition of Bleach and CYA cause TA to stay high? Confused.

Thanks
Todd

 

[jblizzle]

Using the poolcalculator.com, looks like it would take about 54 oz of MA to lower from 7.8 to 7.2. How much did you use?

At the bottom of the calculator shows that, 54oz of MA would lower pH by ~0.7 and TA by 11ppm. Well, the accuracy of the TA test is +/- 1 drop (10ppm). So not terribly surprised that you did not see the difference.

Lowering the TA is a process and can take some time.

 

[JasonLion]

That much acid would have lowered the TA by about 10 or 15, which is lower than the error range on the TA test results. Presumably the TA did go down a bit, but the test simply isn't precise enough to reliably show the difference. In this particular situation the TA test is +-20 (+-10 plus another +-10 for every 10 drops used in the titration).

Lowering TA is a long drawn out process. Don't expect the TA to go down all at once. Keep at it and the TA will come down. It just might take a while.

 

[Richard320]

I'd vote for testing error, myself.

I use a speedstir to do all my tests. The TA test will turn from green to grey then start going back to green. The next drop usually pushes it to pink and if i wait about ten seconds it will go back to grey, and then the last drop will push it to pink where it stays. I think I would have stopped swirling when it went pink. Speedstir is the solution, in my opinion.

 

[tlhwxman]

Thanks Blizzle, Lion and Richard,

@JBlizzle - yep I used about 60 oz of MA. I use the pool calculator for all my amounts. I forgot about the the "Effects of" feature bottom. Thanks for the reminder!

@Richard - I use a speed stir as well. Best purchase I ever made. I get the exact results you do with TA. I stop when it turns red and stays.

Okay...so stay the course and keep the process going. Message received. Thanks again.

Todd