Question about TA before I start borating

[NocturnalDoc]

OK, so TFP says my TA should be 70-90+ since I'm using liquid chlorine. And the Borate Sticky says to adjust TA first. I'm currently at TA 110, which doesn't seem unreasonable, though I don't really know how much "+" is OK on that 70-90+ range. Is there any utility in lowering my TA to say, 80, before I start adding borates (I'll be using MA and Borax)? I do have a bit of pH creep, as my pH went from 7.4 to 7.8 over the past few weeks. Of course, adding MA will lower pH (and TA), but it's supposed to be essentially no change since I'm adding all the Borax as well.

FC 5.0
CC 0
TC 5.0
TA 110
CH 210
CYA 20 (goal 30, getting there)
pH 7.8 (goal 7.5, just adjusted a few min ago)

23000 gal IG, plaster, no regular aeration (though I could point a return to the surface), DE filter.

So, my main question is: Do I need to lower TA to 70-90 before starting the process?

Thanks!

 

[JasonLion]

You don't have to lower the TA first, but I recommend doing it before adding borates. Lowering TA will reduce, or perhaps stop, your PH creep.

 

[linen]

Also, lowering TA after adding borates is more difficult than doing it before.

 

[NocturnalDoc]

OK, so I'm adding MA and aerating. How long does this typically take? I just added MA to get my pH to about 7.0-7.2.

 

[Richard320]

OK, so I'm adding MA and aerating. How long does this typically take? I just added MA to get my pH to about 7.0-7.2.

It depends mostly on how vigorous the aeration is.

With my spa set to max and the blower on, I can lose 50 ppm TA in 3 hours. Or could, when it was high. It's like most things in life - the last little bit is a lot harder than the first big chunk. Aim the returns up, run it all through the spa if you have one, anything to get things churning.

 

[linen]

That should have lowered TA by about ~13 ppm to ~97 ppm. You can estimate this by using the "effects of adding chemicals" section near the bottom of the poolcalculator.com

Aerate until you are up to 7.8 then drop your ph back down to 7.2 and that should drop you down to ~80 ppm TA.

As Richard320 suggested, if you have an attached spa that is a good way, otherwise you can point a return up to disturb the surface and aerate that way. How fast is determined by how much aeration you get and it goes slower as your TA gets lower.

 

[NocturnalDoc]

Thanks guys. All very helpful comments. Unfortunately, I only have one return that will break the surface, and no spa. Maybe tomorrow I'll fashion a hose to a return and get it above the surface.

So, to clarify... the real reason to drop the TA is to eliminate pH rise? So why the recommendation for higher TA for pools with di/trichlor and higher CYA? Does the CYA also stabilize pH?

 

[linen]

So, to clarify... the real reason to drop the TA is to eliminate pH rise?

Yes, and this is a good point...if you were not in the process of adding borates, our advice would probably be to see how much ph rise you get before you go to the trouble of aerating and lowering your TA. But because you are adding borates, experience has shown that you will need lower TA since Borates also act as a ph buffer (independently from the TA) and in addition, your TA will also go up just a little.

So why the recommendation for higher TA for pools with di/trichlor and higher CYA? Does the CYA also stabilize pH?

Trichlor and Dichlor are acidic, so the higher TA buffers the amount of negative ph change that they cause. When cya is higher, more chlorine is needed to keep the pool clean and clear...and if trichlor and dichlor are still being used for the chlorine at point, then more is needed, and therefore the amount of acid they add is also getting higher. It's an ugly cycle