Total Alkalinity and pH

[m100psi]

I read recently, on another forum citing this one, that it is generally OK to let TA levels fall below those recommended if that's what is needed to keep pH down. I haven't been able to find those threads so it would be great if someone could point me to them.

It has been tough to keep the TA up in my 9 month old gunite/pebble pool with no water features. I'll add some baking soda, bring it up to 80-90 ppm, then it will fall back down to 70 or below in a week or two.

I have also found that I need to add acid (31% muriatic) a couple times a week to keep the pH balanced, about 1.5 Q total per week. Since high pH is related to high TA, I wonder if I'm fighting a battle here I shouldn't be. Does it make more sense to let the TA drop and see if the pH stops driving up so fast, or will TA below 70 lead to corrosion?

Thanks,
Matt

 

[YippeeSkippy]

Is this a newly finished pool? New plaster is renowned for requiring frequent doses of MA, which have the side effect of lowering the TA. What is your current TA.....better yet all your test results?
If your TA is 60 or 70 it doesn't really matter as long as you keep your CSI slightly negative. Have you played with PoolMath yet? Either the App or the web version found at the bottom of this page, input all your results and let it spit out a CSI number for you.
This allows you to tweak things to stay "balanced" yet keep your plaster curing properly.

Maddie

 

[m100psi]

Hi Maddie,

Yes, I use the pool math app. Not sure what's considered "new"...the pool installation completed about 9 months ago. Current values are below.

I didn't know about CSI previously, so I just turned it on. Looking back through the records, it's generally well within -0.6 to 0.6, except the time the TA dropped to 40.

Is there a lower limit TA levels should not be allowed to drop below, regardless of CSI?

Thanks,
Matt

 

[mknauss]

Is there a lower limit TA levels should not be allowed to drop below, regardless of CSI?

TA of 50 ppm is when you should get concerned. Below that level pH can get unstable. Our typical recommendation is to raise TA to 70 when you get to 50.

 

[m100psi]

OK, thank you.