Lowest stable TA you've run

[BuckeyeChris]

Playing around in pool math... I am trying to stay slightly negative on CSI to combat very light scaling until I can do a partial drain this winter (high CH).

Current TA is 50. I can try to keep pH down near 7.4, but it will drift again. Or I can get the TA down to 40 and be fine at a pH of 7.6, which will fluctuate much less. Lowering TA by 10 is just as effective as lowering the pH.

I've seen talk of the pH crashing if the TA is too low, so what's the lowest stable TA you've kept your pool at?

 

[duraleigh]

so what's the lowest stable TA you've kept your pool at?

This question bothers me. If you get an answer from someone of 10 ppm, will you take the TA down to 10 ppm?

You are managing your pool by what a computer tells you to do.....same as the pool stores do (yes, I am trying to be a little incendiary....bear with me)

TFP teaches you to manage your pool by adhering to a set of standards we know to work. We want you to learn and understand what those standards are for.

We see it time and time again on this forum, "Help! My pool is green but my numbers are perfect, How is that even possible.?" or, "I followed PoolMath and put in 32.5 oz of chlorine, 14.5 oz of MA and my pool won't clear up? What am I doing wrong?"

If you are experiencing scale, you are letting your pH get too high. Keep it lowered with muriatic and I doubt you will have any further issues with it. I read most all your posts and I know you understand thoroughly what we do, but relying on csi or PoolMath to "fix" your pool takes YOU out of the equation and YOU are the single most important ingredient, not csi.

 

[pooldv]

My TA stopped on its own late last year at 50 and PH right at 7.7/7.8. Some folks have stable PH with TA at 40 and some don't. But, it is worth a shot and easy enough to monitor.

I agree with Dave in most cases on CSI, but if you have very high CH then sometimes you have to take extra measures to offset that.

What is your CSI with TA 50 and PH 7.8?

 

[JVTrain]

Check out the 4th graph in this post: Pool Water Chemistry

Essentially, no matter what TA you are at, the higher your pH is, the slower you'll have carbon dioxide outgassing from your pool. Slower outgassing of carbon dioxide means slower pH rise. So... find a TA level where your pH is stable at 7.6 or even 7.8 and let your pH live at up to 7.8. DON'T constantly try to maintain a pH of 7.4. You'll constantly be chasing the pH rise monster that way. If your CSI is fine at a given TA and a pH of 7.8, let it be unless pH goes above that.

 

[borjis]

As many have said, each pool is different. You need to find a TA that works best for yours.

My last pool liked 80 so I left it there. My current pool had ph fluctuations when I tried TA at 50 (I renovated this one so the water was a fresh fill)

It ended up having stable ph at 80.

 

[BuckeyeChris]

If you are experiencing scale, you are letting your pH get too high. Keep it lowered with muriatic and I doubt you will have any further issues with it. I read most all your posts and I know you understand thoroughly what we do, but relying on csi or PoolMath to "fix" your pool takes YOU out of the equation and YOU are the single most important ingredient, not csi.

If I keep lowering the pH from 7.8 to 7.6 more frequently, the TA will eventually drop to 40 anyway. It's just a matter of "get there now, or get there later".
So this is mostly why I ask; I am certainly capable of keeping the pH lower, but then it will keep lowering the TA. If I can just get to the lower TA, and let the pH be a touch higher where it's more stable, it should be more consistently in the negative. That's just the theory I'm asking about.

CH is around 900
salt around 5200 (3 years of TFP btw, I have to drain due to salt now instead of CYA).
TA 50
temp 90-95

 

[duraleigh]

What is the CH of your fill water?

 

[BuckeyeChris]

5 or 600, IIRC. The pool was filled with it, but has been getting RO water through the auto-fill ever since. Which is still maybe 100 or so, but if I can knock the pool back to 400, I should get a few years in between partial refills.

Which, between that and the high salt level of bleach...maybe I should just use tabs anyway. But that's for another thread.

EDIT: the auto fill is getting softened water, not RO. Frain bart.

 

[JoyfulNoise]

[EDITED]

See this later post - Lowest stable TA you've run

 

[pooldv]

I was curious about salt added by bleach so I did a little Poolmath
3ppm FC adds 5 ppm salt with 8.25% bleach. So, I could see that adding about 1500 ppm of salt per year and with little rain to overflow the pool ever that is a real thing to have to consider. Although, 5000 ppm salt doesn't hurt anything that I am aware of, my pool was there for a year. And you'll likely need to drain some to lower CH after 3 or 4 years anyway, in that climate. Sounds like a good time to convert to SWG.

I would try TA 50 and PH 7.8

 

[JoyfulNoise]

To answer your question regarding the lowest possible TA, you have to realize something - TA is total alkalinity. It is the sum of the concentrations of all species that can accept a proton (or multiple protons) expressed in units of calcium carbonate concentration. So if you have borates or cyanurates (which you do!) in your water, then the floor of your alkalinity is really the concentration at which the carbonate portion reaches zero because acid additions only practically affect carbonate alkalinity (conversion of bicarbonate to aqueous CO2). This is somewhat pH dependent but cyanuartes will make up about 20ppm or so of the TA and the rest is carbonate alkalinity (mostly bicarbonate). So you figure if your TA is 40ppm, then your only about half-way to bottoming out your TA and causing wild pH fluctuations. Cyanurates make lousy pH buffers (limited buffer capacity) and so, if you take away all of your bicarbonate alkalinity, your water's pH is going to crash.

So a reasonable floor for TA is about 50ppm for most pools... you can go lower but you have to be very careful to watch your pH especially if your fill water has low TA.

After some review, it's appropriate to amend what I have written. Chem geek covered a lot of this territory in this previous post -

pH Buffer Capacity

If one were to use the Pool Equations spreadsheet he wrote (Pool Math derives a lot of it's calculations from the math in that spreadsheet but Pool Math is far easier to use for the casual pool owner), you can play with the numbers independently and see how carbonates, borates and cyanurates all affect pH changes (how much acid you need to shift the pH by a certain amount). While it is true that it takes different amounts (concentration) of each buffering species to have similar effects, they all do buffer the pool water. So it is NOT true that carbonates are the only species one should consider. Borates don't have much buffer strength at low pH but cyanurates do. So, even if you used up all your carbonate alkalinity by adding lots of acid, cyanurates would still provide some buffering as well.

However, one still does not want to use up all of the carbonate alkalinity in pool water as it is the primary buffer. So while the lowest possible limit to TA could be quite low, it would be unwise to try to push it down that far. If 50ppm TA still causes too much trouble (acid demand), then adding borates is probably a better and safer solution then trying to artificially push one's TA far below the point of where the fill water is at. In my own pool, my fill water has a TA that ranges month to month but usually around 100ppm (90-120ppm). With my frequency of acid additions, my water tends to settle around 60-70ppm TA. Trying to get to 50ppm requires a lot of acid and it won't likely stay at that level for long without a cover on so I don't push it. By adding 50ppm borates, my pH stability is just fine (my acid addition frequency is about 16oz of MA every 10 days or so).

 

[BuckeyeChris]

SWG is definitely on my radar, but I have no post-filter room on the pipes for it. Maybe if it can be installed vertically.

at 5200 salt, the taste makes itself known just by swimming around. Last year if you took a mouthful of water you'd know it was salt, this is year is obvious from the minute you submerse. It's distracting. But the salt does help with the scaling slightly.