TA finally down but puzzling

[Toddunder]

I have a new-ish gunnite pool (about a year and a bit old). It's a salt-water pool with general results of:

TC 3-10
CC 0-0.5
pH 7.2-8.0
TA 110
CYA 70
NaCl 3200
CH 375

today, in particular, results were
TC 9.0
CC 0
pH 7.5
*TA 70*

So for the past year or so the pH rises over the course of a week or two from 7.2 to over 8 and then I add acid to bring it back down to 7.0-7.2 and the cycle starts over. My limited understanding was that this may be due to the walls of the pool still affecting the water chemistry.

The TA has always been too high so I've been trying to do the "lower the PA and aerate" thing with very, very limited success. In part, since the pH keeps rising by itself anyway, it's been hard to know whether it was working at all.

Two weeks ago the TA was at least 100, closer to 110 (the test turns first purple at 100 then red at 110 using the K2006 Taylor test kit). Today I measured it at 70. All of a sudden. I supposed that's fine (it's within the OK range for my pool and temperature but I think 80 is more ideal). So my question:

What the heck? How did this happen all at once? Did the walls finally stop leaching and this is the result? Do I need to add some baking soda to bring up the TA back around 80?

Thoughts or recommendations? Thanks!

(I also have some calcification on the walls at the water line that's not making me happy but that's a separate question for later and might be related to winter).

 

[Texas Splash]

It's hard for us to know why your A took such a dramatic drop from 100-110 down to about 70. But 70 is a good number. I would not try to increase the TA because with a SWG your pH will continue to float upwards simply due to the cell's aeration. A lower TA helps to prevent pH rising. Many salt pools find their pH stabilizing around 7.8. The calcium you are seeing at the waterline might also be from a combination of the elevated TA and the pH getting up to 8.0. So for now I think you can simply focus on managing the pH (around 7.7-7.8) No more heavy doses of acid required since your TA is already at 70. In fact, if your TA drops to 60 just from normal pH management that's okay as well.

 

[Jimrahbe]

Todd,

Most saltwater pools like their pH to be about 7.8... Adding a ton of acid to lower the pH to 7.2 is almost a waste of time.

We also don't recommend that you try to change the TA just to get a specific number.. As long as the TA is above 50 and your pH is somewhat stable, just leave it alone.

Thanks,

Jim R.

 

[Texas Splash]

I just realized you will probably be closing soon. The only thing that might change is during your closing adjustments, you might bring the pH down to about 7.4-7.6, but that's at closing.

 

[Toddunder]

Thanks, great feedback here.

I was working on lowering TA based on explicit guidance at: What Are My Ideal Pool Levels? - Trouble Free Pool
which shows that 100 or 110 is significantly above the "acceptable maximum". Is that page not correct or is there nuance that I'm missing here? I'm just trying to square that specific range with the comment "We also don't recommend that you try to change the TA just to get a specific number...". I was definitely working to get it below 90 which seemed to the the high end of "acceptable" but I'll admit to ignorance here. That was the only reason I kept using acid to lower the pH to 7.0 or so--to decrease the TA. If that's not necessary we may want to update some documentation in pool school?

regarding closing: no closing! The pool is partially indoors, partially outdoors and I have SIPs that I put over the outdoors section to eliminate most of the loss of head from the winter here (R48!) so i keep the pool going all year.

Great advice about 7.8, though. I'll keep an eye on that and see if it stabilizes there. If it does, that will raise my CSI slightly from the -.035 or so it is now at water temp ~82F to -0.05 which seems better.

 

[Texas Splash]

You're not imaging things. That is the correct page. And while 100 is technically above the ideal or acceptable ranges, and will probably cause a pH to rise faster that desired, the important thing to remember about TA is that if the pH remains stable, then your TA is probably okay. I'd say for most scenarios, when the TA is 100 or more, owners find the pH climbing too fast which is why those recommended levels are a bit lower - especially for salt pools with a SWG (aeration). So it's good you were trying to control it. Now that your TA is around 70, you should be getting close to that "sweet spot" of equilibrium where the TA and pH settle down. Hope that helps.

 

[Toddunder]

Perfect. So the high TA *may* have explained why my pH was always rising so fast (combined with newish plaster pool).

I have gone through ~8 gallons of muriatic acid in the last year or so, so it's not terrible but it's not nothing.

Let's hope this stabilizes things.

Thanks, again, for the educated and thoughtful replies.

 

[Dirk]

By "ichor 30 SWG" do you mean a Pentair IntellliChlor 30?

When my pebble was new, I battled with TA. It finally did what yours did, and it's been stable ever since. Until this summer, when I started a new assault on pH, trying to keep it at 7.4. That just used a whole lot of acid and trashed my TA. I raised the white flag and let my pH go up to 7.8. The acid use went way down, and my TA stabilized at around its normal 60. Lesson learned (that I apparently needed to learn several times). Just as the guys advise: pH in an SWG pool likes to be 7.8+. TA will take care of itself.

Your pH is rising so fast because you're forcing it down where it doesn't want to be. At 7.8 it'll rise much more slowly, and use much less acid.

With newish plaster and an SWG, you'll likely always need to add a little MA. I still need to with my 3-year-old pebble. I solved for that with a Pentair IntellipH acid injector system. It requires an IntelliChlor transformer, and plugs into it, while the IntelliChlor then plugs into the IntellipH's controller. All quite easy to install. So if you do have an IntelliChlor, this might be an option for you. Just mentioning this if you ever tire of dealing with the acid. I fill my IntellipH's tank every couple of months and between it and the SWG I have very little to do with my pool during swim season. Very convenient.

If you're using your IntellliChlor as a stand-alone unit, I think you can only set its output percentage to large increments, like 0, 20, 40, 60, 80 and 100, or something like that? With the IC plugged into the IntelllipH's controller, you'll be able to set the IC in 1% increments, for much finer control.

Full disclosure: because the IC and IpH work together, they both stop working when the water gets to about 50°. I don't close my pool, so I have to go manual with the acid and chlorine for about 3 months or so in the winter. Only once a week, though, so about 12 times a year I have to dose manually. A small price to pay for the convenience I get the rest of the year... If you close your pool, I suppose you won't have to do even that.

So in the spirit of a Trouble Free Pool: let your pH live around 7.8, leave TA alone, get yourself an IntellipH and kick back!

 

[Toddunder]

Thanks for the additional followup.

Yes, it's a Pentair IntellliChlor 30.

The pH was rising, not just to 7.8, but way above 8.0. Hard to measure it but very extremely totally red.

So my main goal with lowering it was, specifically, to lower the TA as described in the article linked. But now that the TA is ~70, I'll just leave it alone. Today I measured 7.5 pH and TA just a bit above 70 (purple red at 70 but completely red at 80). So I think I'm in business here. But I'll happily let it hang out at 7.8. I do wonder if the newness of the plaster just finally wore off.

My SWG is controllable in 1% increments by hand.

 

[Dirk]

The total amount of acid you need to add should go down over time, as the plaster cures. Though you might always need to add some, based on several factors.

How are you able to adjust an IC30 in 1% increments?

 

[Toddunder]

It just does 1% increments. Is that really surprising? Am I citing the wrong model? Photos attached.

 

[Dirk]

My bad, well, we bad. I had asked you if you had an IntelliChlor 30. You said yes. But there is no IntelliChlor 30. IntelliChlor comes in 20 or 40 or 60 flavors, not 30. The iChlor is a different product, which is what you have, not an IntelliChlor. The stand-alone IntelliChlor can't be adjusted in 1% increments (you need a separate controller to do that). Apparently iChlor can be. So thanks to me and you and Pentair's naming conventions for messing all that up. We might have it straight, now... Sorry for the confusion, well, my confusion!