Acid Consumption 2 years post re-plastering

[C4ST]

My pool was replasterd and started up in early July, 2018. It's my understanding that pH tends to creep up after replastering requiring attention and acid addition. But 2-1/2 seasons later, I still seem to be constantly fighting with my pH creeping up. I keep track of acid consumption, and I've added an average of almost 10 ounces per day of 20 Baume Muriatic acid to try to keep my pH down in a reasonable range--i.e., slightly below 7.8. As an example, I'm getting ready to close my pool, and my pH was 7.6 on 10/13, and with no acid addition crept up to 8.1 in six days (10/19). I'm concerned that if I close my pool and stop adding acid my pH will quickly climb to an unacceptable level (it was 8.5 when I opened my pool this spring on 5/13/2020).

Is this reasonable, or am I missing something? What should I be doing about pH monitoring/control over the winter?

Current (and typical) water chemistry is:

pH: 8.1 (as of 10/19--typical is 7.8 or slightly less)
Free Chlorine: 5 ppm
Combined chlorine: 0 ppm
Total Alk: 70 ppm
CYA: 30 ppm
Calcium Hardness: 300-325 ppm

 

[Texas Splash]

Since you are closing soon, I would just do your final pH adjustment and close. It's not uncommon for pH to rise slightly in colder water, but it should settle somewhere in the mid 8.5 range and remain there while the pool is dormant. It's been unseasonably warm across the country, but once your water temp drops it will help to counter-balance the elevated pH. Open as soon as you can next spring though.

From your signature, it looks like this is a non-salt pool correct? so next season you might try a TA of 60 to see if that helps. If you have no unusual aeration in the water, that's about all you can do.

 

[Dirk]

I can't advise about the closing aspect, as I don't close. But I can commiserate with the constant pH-rise. Three years later and my pool still drinks MA. I've given up hope it'll ever stop. It is what it is. I use automation for acid dosing and that pretty much makes it a non-issue for me. pH is now stable all the time. That might be something for you to consider during swim season.

 

[Rattus Suffocatus]

Being in a place that we don't close I might be guessing incorrectly, but the high pH isn't a problem for the gunite pool itself, just the equipment. That's all flushed out and turned off, right? I think I wouldn't worry about it. Just be careful at startup. Be ready to add a lot of acid then.

Or maybe on a warm day in the middle of winter get some water out of the pool, test it and add acid appropriately then. Even in NJ you should get an opportunity once in a while to do this.

I still have to add acid in the winter here in AZ, but the amount needed does go down a bit. (Not as low as the chlorine demand tho. I am burning through like 1.5 PPM right now with the pool covered. I have my SWCG set in the single digit percentages now, and that is with 74F water.) I do have high TA fill and I am constantly battling it to try to get it under 100 and pretty much losing at this point. So I know what you are up against. As it goes up so does the pH.

With a SWCG that makes it scale up faster too. I suspect I'll be replacing cells more often than most.. I don't know what else I can do about it. In the winter though I am going to remove mine.

Anyway, I digress a bit but I don't think you'll do any damage with it creeping up over the winter because the equipment is not running.

 

[Dirk]

...but the high pH isn't a problem for the gunite pool itself, just the equipment.

If high pH contributes to a high CSI, then that is a potential problem for the gunite pool itself. CSI over 0 indicates a tendency for scale to form on the pool's finish. Cold water temp brings CSI down, so in that context high pH could likely be a non-issue.

With a SWCG that makes it scale up faster too.

Again, it's not high pH alone that tends to "scale up" an SWG, it's high CSI. TFP recommends a CSI between -0.3 and 0.0 to combat scale on the SWG plates. Colder water would alleviate that as well. Removing the SWG for the close even better!

 

[ajw22]

A closed pool can get pH into the mid to high 8's. pH rises to reach an equilibrium with your TA. My pH is in the high 8's at opening based on the amount of acid required to get it back into the 7's.

High pH is not a problem since you will have low water temperature. I close my pool in NJ and don't worry about the water chemistry until opening. Been doing it that way for 30 years.

 

[Rattus Suffocatus]

If high pH contributes to a high CSI, then that is a potential problem for the gunite pool itself. CSI over 0 indicates a tendency for scale to form on the pool's finish. Cold water temp brings CSI down, so in that context high pH could likely be a non-issue.

Again, it's not high pH alone that tends to "scale up" an SWG, it's high CSI. TFP recommends a CSI between -0.3 and 0.0 to combat scale on the SWG plates. Colder water would alleviate that as well. Removing the SWG for the close even better!

Once it stops producing it's out until spring for me. I am even going to take the control unit inside so I can clean it up too. I am now trying to run my pool at about -0.2 but it's a battle.

The cold water temperatures should alleviate scaling a bit though as others have mentioned. I am generally a perfectionist myself, and I'd probably add acid periodically when the water isn't frozen at the surface if I lived in that climate again. But I'd also not lose sleep over it if I couldn't.

I did it about once a week in the winter... without the SWCG this winter... I probably will let the TA creep up to the 130 it wants to sit at and then have a marathon to bring it back down in the spring. My pool with a floor system isn't ideal for aeration (actually it sucks for that) and one of the things I want to build over the winter is something to do that more effectively...I probably will use an external sump pump to make a fountain, honestly.

I go from every other day testing to weekly in the winter here in AZ.. once the water is below 60F I have gone to adding liquid chlorine (last winter) every other to third day and been okay as well. So yeah, you can potentially screw up the pool over the winter by neglect but it's a little bit harder... In my case the pool was super stable under 60F.

 

[C4ST]

Thank you all for your input.