Lowering pH - unsuccessful

[Blackdirt Cowboy]

So I’m trying to lower the pH on my newly plastered pool. Fill water tested as such:

CH - 350
TA - 290
pH - 7.2

In the first couple of days, pH rose to about 8.0. I wanted to bring it back down to approximately 7.6. Pool math recommended I add 40 oz of 31.45% muriatic acid to hit that target. I added that and tested a couple hours later to find no change. I added another 32 oz and left the pump on over night. I tested it this morning and still no change in pH.

So I got to thinking, maybe those additions weren’t enough to offset the high alkalinity, so I checked the alkalinity again, and no change.

Any advice or thoughts into what’s going on? My theory is is that my acid additions aren’t large enough to offset the pH rise caused by the new plaster, but I don’t want to dump a bunch of extra acid in there without knowing that, thus driving pH too low.

 

[Texas Splash]

When the pH hits 8.0, then you'll need to use enough acid lower the pH down to about 7.0-7.2. That larger dose of acid will slowly help to lower the TA as well. As long as your TA is that high, that coupled with new plaster will require acid on a frequent basis. Just stick with it and you'll see the TA slowly drop. Once the TA gets down to about 50-70, you should see a dramatic change in the pH.

 

[Blackdirt Cowboy]

When the pH hits 8.0, then you'll need to use enough acid lower the pH down to about 7.0-7.2. That larger dose of acid will slowly help to lower the TA as well. As long as your TA is that high, that coupled with new plaster will require acid on a frequent basis. Just stick with it and you'll see the TA slowly drop. Once the TA gets down to about 50-70, you should see a dramatic change in the pH.

Yes sir, I understand that. But I don’t want to drop the pH quite that low as I’m doing the bicarb startup method and need to keep my CSI around +.5. I guess at my high alkalinity, the pool math calculator won’t be accurate predicting pH change with acid additions, so I’ll just have to wing it and make many smaller additions of acid until I see a drop in pH.

 

[Texas Splash]

I understand that. But I don’t want to drop the pH quite that low as I’m doing the bicarb startup method and need to keep my CSI around +.5.

In that case, I'll ask @Donldson for some chemistry expertise just to confirm the best path forward.

 

[PoolStored]

I added that and tested a couple hours later to find no change. I added another 32 oz and left the pump on over night. I tested it this morning and still no change in pH.

I think your issue is that with that high of a TA, your pH is rising very quickly...and you aren't testing until sometime later. This is allowing your pH to rise.

Make the addition, then test pH 30 minutes after the addition.

 

[JoyfulNoise]

So I’m trying to lower the pH on my newly plastered pool. Fill water tested as such:

CH - 350
TA - 290
pH - 7.2

You sure about your testing ??

Those are highly unusual numbers for fill water. pH that low with alkalinity that high … heck, I’m surprised the fill water isn’t fizzing like a newly opened bottle of Perrier.

Any water you add from your fill source is going to strongly raise the pH and TA of the pool. With new fresh plaster, you can expect the pH to rise within minutes of adding acid.

Buy stock in your local chemical manufacturing plant as you are going to be buying and using acid by the case load. Sorry, that’s just how it is with a plaster pool. You’re in for about a good year to 18 months of battling high pH.

You might consider an automated acid feeder to help manage the chemical additions. Lugging jugs of acid and measuring out doses is going to get old really fast.

 

[Blackdirt Cowboy]

I think your issue is that with that high of a TA, your pH is rising very quickly...and you aren't testing until sometime later. This is allowing your pH to rise.

Make the addition, then test pH 30 minutes after the addition.

This makes sense to me. But I’m no chemist and wasn’t sure how quickly the reactions would take place.

You sure about your testing ??

Those are highly unusual numbers for fill water. pH that low with alkalinity that high … heck, I’m surprised the fill water isn’t fizzing like a newly opened bottle of Perrier.

Any water you add from your fill source is going to strongly raise the pH and TA of the pool. With new fresh plaster, you can expect the pH to rise within minutes of adding acid.

Buy stock in your local chemical manufacturing plant as you are going to be buying and using acid by the case load. Sorry, that’s just how it is with a plaster pool. You’re in for about a good year to 18 months of battling high pH.

You might consider an automated acid feeder to help manage the chemical additions. Lugging jugs of acid and measuring out doses is going to get old really fast.

I’m positive my testing is correct. I ran the test three times. Always got the same pH and was within 10 ppm on the calcium and alkalinity.

 

[Blackdirt Cowboy]

@PoolStored nailed it. I just added a 3/4 gallon of acid and tested again after 30 minutes. pH came down from 8.2 to 7.4 and TA came down from 290 to 270.

 

[PoolStored]

I had posted this to your other thread, not sure you saw it...worth a read...Link-->Lowering Total Alkalinity (TA) Quickly with the Acid Aeration Method

 

[Blackdirt Cowboy]

Yes sir, I saw the link and read it. I’m not concerned about quickly lowering TA until I get through the plaster startup. Depending on how often I have to add acid, I may just let TA come down slowly. If my acid additions become unmanageable, I may look into aeration to drive pH up faster for more acid additions to bring TA down quicker. A last resort would be an automatic acid feeder.

 

[PoolStored]

You got it well in hand...congrats on the new pool!!!

 

[Blackdirt Cowboy]

Man I’m ready for this plaster startup to be over with. I’m adding a half gallon of 31.45% acid a day. pH will be at 8.2 and a half gallon brings it down to 7.6. The next day its back at 8.2. That automatic acid dosing setup is looking better and better.

 

[reggiehammond]

Man I’m ready for this plaster startup to be over with. I’m adding a half gallon of 31.45% acid a day. pH will be at 8.2 and a half gallon brings it down to 7.6. The next day its back at 8.2. That automatic acid dosing setup is looking better and better.

You're going to want to automate somehow as every week during the summer you'll be dumping new high TA water in, causing your pH to rise and you will need to be wary of CSI to protect your SWCG from scale. My TA on fill water is ~200 from my well and it is what it is. Every time I top off manually, I add a gallon of acid.

 

[Blackdirt Cowboy]

I’m now out of the 30 day plaster start up. It required daily half gallon acid doses for the the first couple of weeks. Then I was able to only add about a quart a day for a week. Finally the last week I was able to add 30-40 oz every other day. Through all that time, pH would measure 7.6-7.8 after my acid additions then the next day would be back up to 8.2+. TA has fallen to about 120-130 through the start up process.

Since I’m out of the start up period, today I added a half gallon of acid to bring pH down to 7.2 so I can more aggressively lower pH. I don’t have a particular goal in mind for TA. I just want it to get down to a level where the pool will reach equilibrium at an acceptable pH.

I’ve gone through three cases of acid so far and I’m headed to town tomorrow to get another case. That’s not as bad as I was anticipating, but I’m looking forward to weekly, if not bi-weekly, acid additions.

 

[PoolStored]

When you get TA down it still may take 6-18mos to settle. Would like to hear when yours settles….

 

[Bperry]

I’m now out of the 30 day plaster start up. It required daily half gallon acid doses for the the first couple of weeks. Then I was able to only add about a quart a day for a week. Finally the last week I was able to add 30-40 oz every other day. Through all that time, pH would measure 7.6-7.8 after my acid additions then the next day would be back up to 8.2+. TA has fallen to about 120-130 through the start up process.

Since I’m out of the start up period, today I added a half gallon of acid to bring pH down to 7.2 so I can more aggressively lower pH. I don’t have a particular goal in mind for TA. I just want it to get down to a level where the pool will reach equilibrium at an acceptable pH.

I’ve gone through three cases of acid so far and I’m headed to town tomorrow to get another case. That’s not as bad as I was anticipating, but I’m looking forward to weekly, if not bi-weekly, acid additions.

You can also float some trichlor tablets in there, which will slowly release a tiny bit of acid, which will help keep your pH down.

 

[Blackdirt Cowboy]

When you get TA down it still may take 6-18mos to settle. Would like to hear when yours settles….

Just circling back here to provide you an update. I’m nearly 6 months in and I’m down to adding about 18oz of muriatic acid a week. That will get my pH to 7.5 and by the next week it’s back up to around 8.0-8.2. So it has definitely gotten more manageable.

 

[Newdude]

Try aiming for 7.8. Many of our pools sit there for longer. Imagine any swing, the harder you push the harder it comes back. You're pushing moderately gentle to 7.5 but a gentler push may swing even less.

Thanks for the update !!!