PH/TA Balance Problem

[Woodberg]

I have asked a few questions lately regarding PH rise and TA, but I'm still having a problem, so I thought I would create a new topic to try to get some help.

My problem is that my PH has started to rise rapidly and I need to get it stabilized. My current numbers are as follows:

FC - 5
CC - .5
PH 7.8
TA - 90
CH - 270
CYA - 50
Temp - 92

You might think that a PH of 7.8 doesn't sound to bad, except thats what it was this morning and I added 3 cups of Muriatic acid before work. I got home this afternoon and its already back up to 7.8.

I've been trying to reduce my TA down to 60 per advice on this site. I started at 100 about 4 days ago and thought I had gotten it down to 80. However, when I checked this afternoon, it was back up to 90. I'm being very careful doing the TA test and trying to get even drops every time. I feel pretty confident about the test number.

A couple of factors that I think may be contributing to the problem:

1. The Pool was completed late January (Pebblesheen surface) so its relatively new.
2. I've got a raised spa that spills over most of the day and a waterfall that runs periodically (See pics below)
3. TA is probably still too high based on my level of Aeration
4. Its been extremely hot in Texas and I've been topping off the pool every 2 days. Fill water TA is 110.
5. When I was still using Trichlor pucks, PH was holding fairly steady

I still don't think I really understand how TA helps buffer PH. One question I have is if I am only adding bleach, how can the TA be rising. My understanding was that to lower, TA, I need to lower PH to 7.0-7.2 and then aerate to raise PH back to normal levels without raising TA. I don't think aeration is the problem. In my case, when I do this, PH is back to 7.8 by the end of the day. I just got through adding another 50oz of Muriatic acid to drop the PH back down to around 7.0.

Am I on the right track or could something else be contributing to the rapid rise in PH.

[attachment=1:2p029v9n]Spa Overflow.JPG[/attachment:2p029v9n]
[attachment=0:2p029v9n]Waterfall Deck.JPG[/attachment:2p029v9n]

 

[JasonLion]

New plaster will cause the PH to rise for up to a year after it is applied, so you are still seeing some PH increase from the plaster. Plus, with that much aeration you will see a noticeable PH increase from your only slightly high TA level.

Given your fill water TA level, any time you add water to the pool the TA is going to go up. That may be why you are not seeing as much TA decrease as you would expect.

Adding borates will help slow the PH rise.

Trichlor is acidic, so in effect it was adding the acid for you.

 

[reebok]

come on, you know plaster that new is going to cause the ph rise. you just wanted to show off didn't you?
well I'll take the bait. looks great!

 

[Woodberg]

Thanks for the compliment. We are happy with the way the pool turned out. Seriously though, I wasn't sure how long the plaster would have an effect on the PH. What's weird is that the PH seems to be rising more the last month than it has during the spring. The only thing I can think of is I'm using more fill water because of the high evaporation. I've always had to add a little acid to keep the PH down, but it has really accelerated.

Besides fill water, is there any way that the TA can rise without adding some chemical to make it rise. Right now the only thing I'm adding is bleach. Its a generic brand from the grocery store. I have thought that maybe I should go back to just using Chlorox brand for a while and see if it makes any difference.

 

[MikeInTN]

Bleach won't cause your TA to rise. chemicals, high TA fill water, and new plaster will.

 

[Woodberg]

Bleach won't cause your TA to rise. chemicals, high TA fill water, and new plaster will.

Chemgeek had made a post awhile back saying that some generic bleaches had more excess lye which would tend to raise PH. Would that also increase TA or not have any effect. I'm using a generic regular bleach but the label doesn't say anything about excess lye.

Does new plaster raise TA or just PH? or does it affect both?

I'm just trying to rule out any possible way that my TA can be rising except for fill water. Since I'm not adding anything to the pool right now except for Bleach and Muriatic Acid, I wouldn't think TA would be rising. The reason I think that's important is because I'm trying to lower my TA down to around 60 and if I'm doing something else that is making the TA go back up, I'm just wasting my time.

 

[MikeInTN]

Bleach won't cause your TA to rise. chemicals, high TA fill water, and new plaster will.

Chemgeek had made a post awhile back saying that some generic bleaches had more excess lye which would tend to raise PH. Would that also increase TA or not have any effect. I'm using a generic regular bleach but the label doesn't say anything about excess lye.

Does new plaster raise TA or just PH? or does it affect both?

I'm just trying to rule out any possible way that my TA can be rising except for fill water. Since I'm not adding anything to the pool right now except for Bleach and Muriatic Acid, I wouldn't think TA would be rising. The reason I think that's important is because I'm trying to lower my TA down to around 60 and if I'm doing something else that is making the TA go back up, I'm just wasting my time.

I'm thinking that lye would only raise pH, not TA.

Yes, new plaster will raise both TA and pH (and also CH).

 

[chem geek]

Don't forget that with acids and bases added to water, pH and TA move together. However, the TA doesn't move that much. With your pool volume, it takes about 6-1/2 cups of Muriatic Acid (31.45% HCl) to lower the TA by 10 ppm and the pH would go from around 7.8 to 7.15 with such acid addition (if nothing else were happening). So seeing changes in TA of around 10 ppm would not be unusual and is the resolution of the TA test anyway.

For plaster (or equivalent) curing, it doesn't take much to have the pH rise a lot. If you started at a pH of 7.4 and TA of 85 ppm, then plaster curing that would raise the Calcium Hardness (CH) by 5 ppm would also raise the pH to 7.8 and the TA to 90.

The high amount of aeration increases not only the pH rise, but also evaporation rates so whatever is in the fill water gets added to the pool. Your pool water is hot so if the air has low relative humidity, then evaporation is probably quite significant. I suspect that this is the primary source or your TA rise over time. If you've got 1/2" per day evaporation (which is high, but with all of your aeration and high temps, it's possible), then with a 4.5' average pool depth this is 28% of your pool water volume per month. The TA would increase by about 30 ppm per month from this effect.

The excess lye in some bleach can lead to a small pH rise over time, but the change in TA would not be noticeable since the pH rise is small. With a typical off-brand bleach, the pH rise after 30 ppm FC cumulative addition and usage is around 0.2 units. So that might be over two weeks. It's not a huge factor compared to other factors.

Richard

 

[Guest]

You have new plaster, a lot of aeration, an ozonator that added even more aeration, and fill water with high TA. Any one of these will make the pH rise. You have four. Once the plaster cures fully (this takes about a year) you will eliminate one of the problems but the other three will remain. Your option is to use trichlor, which is acidic, so it's the same as regularly adding acid to the pool BUT you will be doing drains and refills on a regular basis to keep the CYA in line and, believe me, that is MUCH more difficult than keeping the TA low and pH in line.
This link should help explain a bit more about TA and pH and how they interact.
ta-what-is-it-really-t4979.html

Read it through a few times until you understand it.

Using a cheaper bleach with a higher NaOH content is not going to cause any appreciable rise in pH. Your pH rise is from the factors I mentioned above. Right now I would have to say the biggest factors are the new plaster (which all you can do is waiit on and keep pouring in acid) and the high TA (which you can lower down to about 60 ppm.) Turning off the water falls and oznators will also help but are probably options you don't want to do.

 

[Guest]

I'm thinking that lye would only raise pH, not TA.

It would raise both since it would convert some of the carbonic acid in the water into bicarbonate ion, which is what TA is. However, depending on how much the pH changed, the change in TA migh be below the precision of the TA test so it might not be apparent.
Remember TA moves with pH because pH from (high to low)changes carbonates to bicarbonates to carbonic acid and vice versa. TA is the bicarbonates and carbonates in the water (for all practical purposes). Carbonic acid (carbon dioxide in water for all practical purposes) is NOT part of TA nor it is not measurable by our TA test.

 

[MikeInTN]

I knew I should've paid more attention in chemistry back in college. Note to university - NEVER have chemistry @ 0800 in the am!

chem geek and 'bear - thanks for the explanations.

 

[Woodberg]

OK, thanks for the replies. I'll read this through about 10 times tonight and try to understand it. In the meantime, I'll keep ading acid and continue with the aeration and try to get my TA down a little bit more and see how the pool balance reacts.

 

[frustratedpoolmom]

OK, thanks for the replies. I'll read this through about 10 times tonight and try to understand it. In the meantime, I'll keep ading acid and continue with the aeration and try to get my TA down a little bit more and see how the pool balance reacts.

I've read it 100 times and don't understand it.