pH and TA Suddenly very low

[cjs]

I added Borates to my pool about 3 weeks ago, and now sit at give or take 50 ppm. I have always had a problem managing the TA in my pool because the fill water has TA in excess of 300. So, for the past year or so, I have always added muriatic acid whenever I top off my pool to first bring pH down to 7.2.

Everything has been fine until today.

On Thursday, I added water. Prior to fill, my readings were as follows:

FC 4.5
TC 4.5
CYA 40
pH 7.5
TA 70-80

So, as the fill water was going in, I added about 14 oz of acid, which is less than the pool calculator said was needed to bring it down to 7.2. I never tested again until today, and here are the current numbers:

FC 3.5
TC 3.5
CYA 40
pH is less than the lowest reading on the Taylor Chart
TA came in at 40

It's almost like someone snuck in and poured a bunch of acid in my pool while I slept!!!

OK, moving on:

1) My pool has an always-on spa spillover. I just turned on the additional waterfalls as well as the spa jets as that has always been very effective aeration to raise the pH.

2) I don't really want to increase my TA with any additives as my fill water takes care of that for me.

So, my questions:
1) Are the TA or pH numbers are accurate? Or, does one of those numbers being off effect the test integrity of either or both of those?

2) Is it OK to have low TA for a couple of weeks while I wait for the fill water to bring it back up?

3) If the answers to those 2 questions are yes, should I do anything to manage my pH during that time...or just assume it will be off for a while?

Any thoughts on how this could have happened or what I need to do would be greatly appreciated.

Thanks,
Craig

 

[JasonLion]

The TA test is +-10 and quite reliable. The PH test is a little subjective and sensitive to high FC levels, but otherwise quite good. The two tests don't really interact. Chances are your test results are correct.

Aeration will be less effective than usual because the TA is so low.

Low TA makes it much easier to change the PH. The danger with low TA is that the PH can change right out of range if you aren't careful. Having borates in the water will help control that, as the borates act as a PH buffer along with TA. Given that you have borates in the water, you should be alright, though that is as low as you should let TA go.

 

[cjs]

OK...I could leave this open and see if the brains on this board would come up with the solution....but I figured it out!

See, I have 2 bottles that are similar (the ones you get from the pool store for water samples). I use one for samples...and recently, I've been using the other 18 oz bottle to measure and add my acid to the pool. It seems I used the same bottle to get this test sample as I used to add the acid on Thursday...and it appears there must have been a little acid left in the bottle!

With that testing quality, I may go fill out an application for a job at the pool store!

Test numbers with clean water bottle:
TC 3.5
FC 3.5
CYA 40
pH 7.6
TA 70-80

I'll try to do better next time!

 

[chem geek]

Glad you figured that one out! That would have truly been a strange mystery as to how the pH could have dropped so much.