Running pH 7.8-8.0 vs chasing the acid dragon.

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lalittle

Well-known member
Apr 4, 2011
184
Los Angeles, CA
My pool's pH is constantly rising. I've tried for a few years to figure out why this is happening, but at this point I've kind of given up for the time being. It's not new plaster, I don't have any water features, I've played with the jet directions, etc. For whatever reason, the pH is just going to rise.

If I knock the pH down to 7.5 or so with muriatic acid, it rises back up to around 7.8 pretty quickly, then the rise slows down, creeping up to 7.9 or 8.0. If I continue to let it go, it still rises, but much more slowly.

I'm therefore wondering if I should run the pool in this 7.8 to 8.0 region rather than constantly fighting to keep it down in the "recommended" 7.4 to 7.6 range, which requires a couple/few doses of acid every week. In other words, if I wait until the pool is fully 8.0 before adding acid, and then only bring it down to 7.8 or so, it will reduce both the cost and the time of adding MA all the time. What I'm unclear about is how "bad" this is. I know that chlorine is more effective at lower pH, but I don't have any feel for how much difference in Cl effectiveness is made by any given rise in pH. At 8.0, what happens? Just how poorly does the Cl perform? Will this be noticeably harder on our eyes? My CSI will be higher due to the higher pH, but I'm wondering if it might be an equitable trade-off to run it a bit high (in the "potential scaling" range) in order to greatly reduce acid usage.

I just don't have the point of reference needed to make an informed decision here.

Thanks for any feedback here,

Larry

This is a plaster pool, about 22K gallons, and I use only liquid Cl. My general specs at the moment (Taylor K-2006):
FC - 5
pH - 7.7
TA - 80 (drops as I add acid)
CYA - 40 (will be increasing to 50 to 60 for summer)
CH - 700
Salt - 1800
Temp - 70
 
There are several small misunderstandings here, hopefully we get those smoothed out and we can get your pool much more stable.

PH goes up primarily due to TA being too high. I recommend letting TA go down to around 60 and letting it settle there. That will reduce the PH drift.

Second, we recommend PH be around 7.7 to 7.8 as an ideal. That will also help the PH be more stable.

Third, chlorine being less effective at high PH is only really true when there isn't any CYA in the water. As soon as you start using CYA that effect becomes so small it can be ignored completely.

You do need to keep an eye on CSI. Lowering TA will help with that a little. Not letting PH go up to 8.0 will also help. If CH keeps going up you may need to get more aggressive with keeping a lower PH. Sadly that is just the way it is.

A PH of 8.0 isn't the end of the world or anything, though I do worry about your fairly high CH level. High CH plus high PH tends to make CSI dangerously high.
 
My CH was actually MUCH higher. It was north of 1200, but after some drain/refills to bring both it and the CYA down, it's down to a much more manageable 700. I don't think it's going to climb since my fill was only in the 200 to 300 range the last time I checked.

If I try to keep my pH much lower, my TA ends up going REALLY low. When I was bringing the pH down to 7.5 or so with each acid addition, my TA dropped to 40. I actually didn't notice any difference in the pH rise even with TA this low -- it still rose steadily. If I add acid every time the pH gets to 7.8, the TA will eventually come down. The TA only seems to stay stable if I let the pH go all the way to about 8 before adding acid.

I've generally tried to keep my CSI as close to 0 as possible, but I've made concerted efforts to keep it between 0.3 and -0.3. I'm wondering if I should target a higher number in order to lower acid consumption. How "bad" is it to simply shoot for staying under 0.6? Going over 0.3 makes me nervous, but giving myself a higher range to work with would make things a lot easier.

You said you were a bit worried about the CH being so high with a high pH, but do I understand correctly that if the calculator shows my CSI as staying in a safe range, there's no problem with running a pH of 8.0? In other words, is the CSI calculation a reliable indicator that everything is fine in this respect?

Thanks again,

Larry
 
I am so glad you asked this question because I was going to ask the same thing. My ph was rising a lot but now it seems to have settled down since my plaster cured. I have waterfalls and a SWCG so I know it will rise but it has slowed down a lot. I was going to ask if I should keep knocking it down when it hit 7.8. I will watch it and see how long it takes to go above this level. I used to easily climb above 7.8 within a few days. Now after two weeks it doesn't seem to make it past 7.8. I am going to hold off on adding acid until it gets close to 8 and see how long it takes. I could save a lot in MA costs. Thanks for posting.
 
I suggest you play with poolmath a bit. Plug your current numbers into the now column and then play with the target. See what happens to the CSI when the water warms up to 80 or 85. Let the pH rise to 8. Figure the CH is going to raise through evaporation. See how each parameter affects the CSI.

You're going to get scale if you're not careful. Also, figure the refill water will raise the TA. Test it to be sure. I've found that once I get TA down to 60-70 that things stabilize. I've also learned over time how much acid I need to add for each inch of water I add to the pool, and I just pour that into the stream while I'm adding water.
 
How "strongly" is it recommended to keep the CSI in the 0.3 to -0.3 "balanced" range vs the 0.3 to 0.6 "potential to become scaling" range? If I could let the CSI go above 0.3 (but stay below 0.6), it would make things a LOT easier on me.

Thanks,

Larry
 
Not speaking for anyone else, but it's very important to watch it with your pH, TA and high CH. Richard is right, plug in the numbers and watch it. He knows, because he's been down the CH scaling road. Mine is very high too, so we are in the same boat in that regard. My well is 700, so I am very strict on my numbers. Only a year in, but I'm doing very well on control.
 
With a SWG, CSI at 0.3 to 0.6 is problematic. Without a SWG, it is alright, however you need to be really certain you aren't going to go over. The key is that left alone PH tends to go up. So if you are in the high range and couple of days of inattention and you can have scaling. Given you pay enough attention and make sure the PH never gets out of control, then fine. But it is much safer if you give yourself some safety margin.
 
lalittle: I have had my own battles with the acid dragon over the last 18+ months since my install. One thing that seems to have helped is increasing my CYA. My finish installer gave me suggested chemical ranges that were pretty close to what the Taylor kit recommends. The one big difference between those recommendations and the TFP method seems to be CYA level. TFP = 60-80; where Taylor and my finish installer say 30-50. I started using the TFP method in October, and by raising my CYA, my acid demand has gone down a lot.

Now the other factor is that my water temp was a lot lower through the fall and winter, so that certainly helped. We are back into the mid 80's now, and soon 90's, so I will see if it continues.

One last thing I may try is adding borates. If you read the thread on adding borates, one of the benefits is more stable pH.
 

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Note that the raising of CYA only reduces the acid demand in SWG pools and the reason is that it lowers the chlorine loss rate (even proportionally keeping the FC/CYA ratio constant) and that lets one turn down the SWG on-time and that reduces the rate of pH rise that is due to the increased aeration from hydrogen gas bubbles from the SWG and from any outgassing of undissolved chlorine gas from the SWG.
 
MWigs -- on top of what chem geek said, your pH stabilization could also have been caused by the fact that, if I understand correctly, your pool was new. New plaster causes pH rise, and from what I understand it can take about a year for this to stabilize, which seems to line up with your time line.

I've definitely read a LOT about borates and considered them on more than one occasion, but in the end I didn't end up trying this because even though it slows pH rise, it does not reduce acid demand since more acid is required to effect pH. In other words, you add acid half as often, but you need twice as much to move the pH the same distance, so the actual demand stays the same. I may still try it, but for now I elected to just keep things on the simpler side.

Thanks for all the feedback here,

Larry
 
JasonLion said:
With a SWG, CSI at 0.3 to 0.6 is problematic. Without a SWG, it is alright, however you need to be really certain you aren't going to go over. The key is that left alone PH tends to go up. So if you are in the high range and couple of days of inattention and you can have scaling. Given you pay enough attention and make sure the PH never gets out of control, then fine. But it is much safer if you give yourself some safety margin.
Click to expand...

When you say "never gets out of control," do you mean never goes over 0.6? I could probably keep it below 0.5 or even 0.4 or so pretty easily -- it's keeping it below 0.3 that's difficult since this requires a lower pH, which requires a lot more acid and a lot more frequent additions, which in turn drives the TA down really low.

I'm jealous of my neighbor whose pH is really stable at around 7.4.

Thanks again.

Larry
 
As long as CSI never goes above 0.6 you should be fine. The "out of control" reference is to PH, which will go up to 8.4 or higher if you ignore it for long enough, and typically if that happens CSI will go above 0.6 and there could well be problems.
 
Thanks.

One other clarification:

When you said in an earlier post to run the TA at about 60, were you talking about the raw value, or the value that's corrected for CYA as per the Taylor instructions? If you meant to use the "corrected" value, than I'm already down in that range since my raw readings are around 75 to 80 by my best estimate, and the CYA correction drops this by about 15 points.

Thanks again.

Larry
 
No, the other way around. The corrected value is only used for calculating LSI, which we don't even use any more. The number direct from the test kit is the "real" number.

More technically adjusted TA is a rough estimate carbonate alkalinity, while TA is total alkalinity. For our purposes all that matters is TA straight from the test kit.
 
If you are interested in the rate of carbon dioxide outgassing that leads to pH rise, then the carbonate (adjusted) alkalinity is what is relevant. If you are looking a pH buffering, in particular its capacity preventing a pH crash from pH getting lowered, then Total Alkalinity (TA) is what is relevant. There is no single magic TA level where your particular pool will slow down the pH rise to the point that is tolerable for you. There is a theoretical point where such pH rise, at least from carbon dioxide outgassing, will stop completely, but it's at an impractically low TA. In practice, the outgassing slows down considerably before that point.

Specifically, to stop the pH from rising you'd have to have the carbonate (adjusted) alkalinity down to the following levels at the pH indicated:

pH . Carb.Alk.
7.0 ....... 3.5
7.1 ....... 4.4
7.2 ....... 5.5
7.3 ....... 7
7.4 ....... 9
7.5 ..... 11
7.6 ..... 14
7.7 ..... 18
7.8 ..... 22
7.9 ..... 28
8.0 ..... 36
8.1 ..... 46
8.2 ..... 58
8.3 ..... 75
8.4 ..... 96

Fortunately such extremes are not needed in practice.
 
My gears are turning here, wondering why the op is getting such a persistent pH rise with no SWCG and long since cured plaster.

Could it possibly be somewhere in the plumbing that there occurs a high rate of turbulent water due to a minor constriction, or a wacky elbow setup, or tee, or even a reducer causing some sort of cavitating? Thus inducing a pH rise like one would see with a water feature, or SWCG.

Maybe a suction side leak that's sucking in air, cuasing aeration?

A possibly silly question, even though the plaster is only 15yrs old, if there were some sort of breakdown occurring, could this cause a pH increase? I'm thinking no, but worth a shot. :)

Lastly, could some sort of "mystery chemical" still be present, in-spite of the partial drain and fills, causing pH to rise?

Just some ideas... puzzling indeed. :confused:


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