How precise does TA need to be?

[TimS]

I put a new vinyl liner in my pool at the beginning of September. I'm still trying to get the TA in line. (I'm not yet using BBB, but plan to for closing and next summer. I hadn't heard of BBB until after I had the pool filled, and had started chlorinating with lithium shock and trichlor.)

My starting TA (tap water) is over 300. I've finally gotten it down to 140. I've been aerating for several days, and have been keeping pH between 6.8 and 7.8. When the pH gets above 7.5, I add more acid. Typically this drops pH to 6.8 or 7.0, and a few hours of aerating brings it back to 7.0 or 7.2. It takes quite a bit longer to get from 7.2 to 7.5 than it does to go from 6.8 to 7.2.

The recommendation in Pool School for TA in a vinyl, bleached pool is 70-90+. OK, how high is '+'? Is 140 an acceptable level or do I need to bring it down further? What's the impact of high alkalinity when closing, and is 140 actually high?

As of this morning:
CH - 200
pH - 6.8-7.0
TC - 5
TA - 140
CYA - 80 (this number is actually a few days old. I didn't test this one this morning.)

These numbers are from an HTH drop kit. I don't have my TF100 yet

So far, I've added about 10lbs of dry acid, and 2.5 gallons of MA. Based on the current rate of change, it will probably take another 1-1.5 gallons of MA (and another week) to get under 100.

TIA

 

[H2O_Keeper]

The biggest thing about a high TA is that your PH will drift up more if it is not in the recommended TFP ranges. I have high TA in my fill water as well and after adds and I get up to 150 I find myself adjusting the PH 1x a week to lower with MA. When I have it at 80 I have to adjust it maybe once a month. IF you are about to close for the winter I would not worry about the TA till the spring.

Also as a side note I see the same thing with a fast PH rise when its low 7's and slow above 7.2....I just hit it at 7.2 and take it a little below 7.0 and keep doing it. I have to add acid more often but I get it done quicker.

 

[frustratedpoolmom]

140 is not that bad, unless you are using an SWG. If you experience rapid PH rise, then lower it further, but unless it causes a problem for you in the PH department, I doubt you will have an issue. My TA was rock solid 120 for two years and it did nothing to my PH.

I would suggest that with the TA of 140, if you close with your PH around 7.0-7.2 you should be fine when you open in the spring, that it's okay to close at that level. Shouldn't be a problem.

 

[duraleigh]

Typically this drops pH to 6.8 or 7.0, and a few hours of aerating brings it back to 7.0 or 7.2. It takes quite a bit longer to get from 7.2 to 7.5 than it does to go from 6.8 to 7.2.

Yeah, if you are around to test it, the TA reduction will go quicker if you stay between 6.8 and 7.2. As I,m sure you know, not a good practice to go below 6.8 during the process.

 

[TimS]

Thank you all. That helps.

Yeah, if you are around to test it, the TA reduction will go quicker if you stay between 6.8 and 7.2. As I,m sure you know, not a good practice to go below 6.8 during the process.

Are you saying that MA is more effective at lowering TA if the pH is lower to begin with? I don't really have a handle on the relationship between pH and TA yet, only what I've read in Pool School and the knowledge imparted by the people on this board. I didn't pay enough attention in high school chemistry, and even if I had, it's been a day or 10,000 and I would have forgotten it by now.

On a semi related note, is it possible to lower pH without lowering TA? Since acid lowers both, but aeration raises pH and not TA, is is possible to get a high pH that needs to come down but to have a TA that is already low enough that you don't want to lower it further? If so, how would you fix it? I'm thinking about next summer. The kids love the fountain, but this summer I didn't know it would change pH. I didn't run it enough to matter, but since the kids have discovered it, they really want it on a lot.

 

[frustratedpoolmom]

Yes it's possible. And you are correct, acid lowers both.

You would lower the PH down to 7.2 ish and then use Baking Soda to raise the TA.

When raising PH and/or TA:

baking soda - raises TA lots and PH a little
borax - raises PH lots and TA a little
washing soda/soda ash -raises PH lots and TA some
aeration when TA is high - raises PH without changing TA

 

[TimS]

Yes it's possible. And you are correct, acid lowers both.

You would lower the PH down to 7.2 ish and then use Baking Soda to raise the TA.

When raising PH and/or TA:

baking soda - raises TA lots and PH a little
borax - raises PH lots and TA a little
washing soda/soda ash -raises PH lots and TA some
aeration when TA is high - raises PH without changing TA

This quote from Jason looks familiar, but I don't recall where I might have seen it. Is it somewhere in Pool School?

 

[frustratedpoolmom]

Not sure - I have it bookmarked from an earlier post. The basics of it get repeated enough, probably why it's familiar.

 

[TimS]

That quote is one of the things that I now have posted inside my supply cabinet where I can find it easily. Thanks.