TA Homeostasis

[spoonman]

Curious about my TA’s movement related to Stenner use for pH/acid control.

I recently converted my pool’s Stenner pump from chlorine to acid. This has been a smashing success overall. The pool has always had fast upward pH drift, but now with the Stenner the pool is holding rock solid at 7.55.

That said, I have been watching my TA during this time and it is slowly moving downward starting from TA 85 (2 weeks ago) down to TA 65 currently. I don’t mind if it drops a bit more, but don’t really know how low the TA will go? How can I keep dosing the required amount without sending TA off the cliff?

 

[duraleigh]

Pool School - Lower Total Alkalinity

 

[Jimrahbe]

sm,

You are good as long at your TA does not go below 50...

I suggest that you run your pH at 7.8... There is no reason to shoot for 7.5 and it will just require more acid. The more acid you add, the lower it will drive your TA.

Thanks,

Jim R.

 

[Dirk]

When I was manually battling pH down to low-to-mid 7s, the TA got down into the 50s. When I started auto-dosing acid, and settled on 7.7 or 7.8 for pH, the TA actually came up a little.

 

[spoonman]

sm,

You are good as long at your TA does not go below 50...

I suggest that you run your pH at 7.8... There is no reason to shoot for 7.5 and it will just require more acid. The more acid you add, the lower it will drive your TA.

Thanks,

Jim R.

Here in Arizona, the CH is very high (mine is currently 700+) so lower pH/TA is required to keep CSI neutral. A pH of 7.55, TA65, temp of 73, and CH of 725 puts my CSI at -.04 which is only slightly negative and keeps the massive CH in the pool from becoming a ring on the tile.

Presumably I could reduce my acid dosing amounts as the TA drops lower (reduced demand) or let the pH sit a bit higher with the lower TA.

 

[Dirk]

Here in Arizona, the CH is very high (mine is currently 700+) so lower pH/TA is required to keep CSI neutral. A pH of 7.55, TA65, temp of 73, and CH of 725 puts my CSI at -.04 which is only slightly negative and keeps the massive CH in the pool from becoming a ring on the tile.

Our Arizonian's will have to describe how they deal with that dilemma. I have CH350 fill water, so I realized early on I'd be facing some similar issue. I solved for that before it ever became one by connecting my auto filler to my water softener. My CH is still well under 400, so I'm able to run a higher pH and still maintain my negative CSI (almost a year now and not a spec of scaling on my tile).

The combination of water softener, SWG and acid doser has so far been worth their trouble and expense.

I don't think I've completely eliminated CH-rise, but it's very slow, and on a par with my salt-rise (which every pool is subjected to). I figure I'll take care of both periodically with minor water exchanges.

 

[spoonman]

I think a Softener is in my future. Matt had suggested this in another thread and it seems it would help tackle a number of items. I really like having fixed variables and having CH constantly on the rise can make achieving neutral-ish CSI a moving target. A softener could allow allow me to run a higher pH, which would probably keep TA more flat instead of trending downward.

For here err and now, I haven’t been using the Stenner for acid long enough to test scenarios, but I suspect that as my TA drops I can dial back the acid dosing to keep both factors balanced (reduced acid demand = less acid added = flat TA).

 

[Dirk]

Sounds like you're on the right track...

My pool and tile were covered in scale when I bought the house. The now-fired pool guy must have let the CH get completely out of control. Since the resurface and tile blasting, as I said, I haven't seen a spec. The softener has made a huge difference, as I have both "before and after" real-world use cases to back up that claim (at least in my pool, anyway).