Total Alkalinity question

[CarolD]

I just went back to reread the Pool School posts about recommended TA levels and now I have questions.
Background: I had been keeping my TA around 80 and letting my PH creep upwards to 8.0 before lowering it with MA. With fairly high water temps in my area, that resulted in a positive CSI (generally +0.1 to +0.3). I noticed what looked like scale, and got some advice here to keep my CSI on the negative side.

As a result, I have lowered my TA to 60, and now I am keeping my PH in the 7.4 to 7.6 range. That gives me a CSI in the -0.1 to -0.5, which the pool math app tells me is OK. I have found that the lower TA allows me to adjust my PH less often, and unless I'm imaging it, the scale problem is diminishing.

Three questions:
1. Is it OK to keep my TA at 60, below the 70-90 recommended for my plaster finish? At one point it had gotten down to 50, but I added some baking soda to bring it back up to 60.
2. Is it possible that the more acidic water (7.4 to 7.6) is dissolving the scale, or is that my wishful thinking?
3. Is it OK to maintain my PH at this lower range long term?

Test results from tonight: FC 6, CC 0, PH 7.4, TA 60, CH 270, CYA 40, CSI -0.40, Temp 85

 

[YippeeSkippy]

1- absolutely fine to be 60. This is one way to slow down pH upperward creep. No lower though, ok?
2- yes when folks have scale risk we tend to suggest letting the pH stay at the lower end of recommended levels.
3- Yes! The suggested range for pH is 7.2 to 7.8.

Maddie

 

[RMcGirr83]

I believe 50 is the lowest your TA should go.

 

[ajw22]

TA of 50 is ok if it naturally goes there. I would not force lower TA to 50.

At TA of 60 plaster pools often find a natural equilibrium between pH and TA that works well.

 

[CarolD]

Thanks for the reassurance on my TA!

Is it possible that with the lower PH in my pool, I could be seeing the scale dissolve? The problem seems to have diminished somewhat from a few months ago. Is that just my wishful thinking?

 

[mknauss]

A CSI less than -0.3 for an extended time can dissolve scale back into the water. It is not quick.