Target TA level

[rinaldok]

Is it a fool's errand to try to lower/maintain a TA of 70 when the fill water is 140?

My "ideal" chemistry requires a low TA. I tend to have high pH, so I wanted to slow the pH rise cycle with borates. I wanted to get the TA to a target number before adding the borates. The target chemistry looked like this:

pH: 7.8
TA: 70
CH: 400
CYA: 80
Temp: 86
Salt: 3000
Bor: 40

CSI: -0.11

With those values, it would allow for water temp 70F+ without any issue, and for winter months I would keep the pH around 8.2 to offset the CSI drop from the lower water temp.

The TA is going to creep upward with evap/fill water, should I rely on my small, periodic MA additions to counter that and hope it holds steady?

I posted a thread earlier where I was trying to lower my TA by cycling my pH down to 7.0 to tick the TA down (I'm down to approximately 80-90 from 140 after 4 cycles). This was apparently causing my CSI to go too negative and now my CH is notching up, possibly due to leeching some calcium from the plaster. So I won't be doing that process anymore, I'll be going for more gradual reductions with pH reductions to around 7.4 and it will just take longer to bring the TA down to target.

But I'm wondering what the long game is here... thoughts?

 

[ajw22]

@mknauss is best to advise on how to manage SouthWest pool chemistry.

 

[Texas Splash]

TA can easily creep-up with fill water. Some parts of the country have a fill TA of 400+. Just one of those things we have to address with acid periodically. Naturally, the more you have to refill, the quicker TA can increase. But with consistent management you'll be okay, and you still have a wide range to use. You understand how water temp, pH, TA, and CH impact overall CSI so that's good. Also remember that a wide swing outside the ideal CSI range doesn't result in immediate impact to plaster. In most cases it takes months. Not so sure the CH increase was from the TA lowering process as opposed to your local hard water though. You have an SWG so the pH is naturally going to climb to the upper 7s. Anything you can do to control that is good. Also, in my quick poolmath check I show your CSI at -0.01 versus -0.11.

 

[mknauss]

I don't use borates. I find in the summer I add acid about twice a week lowering my pH from 7.6 to 7.2 and that keeps my TA right at 70 ppm. Our fill water is 130 ppm TA and I add about 60-80 gallons (right at 1% or more of the pool volume) each day during the summer.
My CH is nearly always (except shortly after a water exchange) higher than 400 ppm CH. And I do not mind a more negative CSI as the SWCG stays clean and I have a fiberglass pool (though with a grouted tile line, though that does not show any issues with the slightly negative CSI).

I know others use borates. It does not reduce the amount of acid you use, just how often you add it.

You state your CH is creeping up - that is very normal. Or do you use softened water for make up water? If so, that is CH free but does nothing to the TA.

 

[TheMerk]

I'm no expert, but I've got my TA pretty steady around 70, with the fill water being 110.

I pay attention to the CSI after entering all values into Pool Math, and I'll lower the pH to whatever value will make the CSI -.3><0. I test every 2 days.

For example, today's pH was eyeballed higher than 7.5 but not quite as dark as 7.8, so I called it 7.7. The CSI tab in PM told me that lowering pH to 7.4 would take my CSI to less than -.3, so I went with lowering to 7.5 which would make my CSI -.23 (I'm doing all of this from memory.)

Naturally lowering the pH over time like this, but not lower than CSI -.3 will drive down the TA while not causing the CSI to rise.

 

[rinaldok]

Also remember that a wide swing outside the ideal CSI range doesn't result in immediate impact to plaster. In most cases it takes months.

Noted. Another member was helping me in that thread and posed it as a possibility, as well as that I could be dissolving some scale. He was clearly more knowledgeable than I, so I will take his advice not to deep cycle the pH as aggressively as i was. I don't have much visible scale, but that doesn't mean there isn't any. I had asked why my CH might be increasing unexpectedly when my only treatments to the water have been the deep pH cycling for the TA reduction.

Not so sure the CH increase was from the TA lowering process as opposed to your local hard water though.

My autofiller is on soft water, and we haven't had any rain and there are no external water sources to get into the pool.

You have an SWG so the pH is naturally going to climb to the upper 7s.

Yep... and I battled high pH even before I added the SWG.

Also, in my quick poolmath check I show your CSI at -0.01 versus -0.11.

You forgot the borates.

 

[mknauss]

My autofiller is on soft water

Add that to your signature.

 

[mknauss]

Do remember that you can get some CH carryover from water softeners if they are not regenerating soon enough.

 

[rinaldok]

I don't use borates. I find in the summer I add acid about twice a week lowering my pH from 7.6 to 7.2 and that keeps my TA right at 70 ppm.

I find myself adding acid every 2 days as I'm always back up to 8.0 very quickly. Just trying to temper that a bit.

I know others use borates. It does not reduce the amount of acid you use, just how often you add it.

Yessir, understood. That's exactly what I'm aiming for -- less often.

 

[mknauss]

I find myself adding acid every 2 days as I'm always back up to 8.0 very quickly. Just trying to temper that a bit.

Once you get your TA to 70 or so, that will lessen. I assume no water features.

 

[rinaldok]

Once you get your TA to 70 or so, that will lessen. I assume no water features.

Correct, pool is just a basic hole in the ground with water in it.