rising ph levels

[chem geek]

My comments in bold in your quoted post below.

Thanks for your very interesing post. I want to learn more about this, because not too long ago I made a similar post about pH increasing and was told to increase my TA from 80 to 100 - 125. Here is a link to that post: http://www.poolforum.com/pf2/showthread.php?t=3715.
Thank you so much for including this link. The advice that was given to you was correct for the problem you described at that time because a large pH shift at the lower TA of 80 will get reduced (somewhat) at higher TA because higher TA buffers the water to make the pH move less when there is a "push" to make the pH move (in your case, from base to increase pH). TA can be confusing because having a low TA makes your pool more easily change in pH, but a high TA makes your pool more likely to rise in pH from outgassing carbon dioxide. With more info, a "balance" can be obtained though it will still result in a rise in pH, but will hopefully lower the amount of acid you need to add each week.

I do not have any water features that would increase aeration and I normally try to keep my return flow so that it does not splash. I have read on this forum that splashing can decrease TA, so I have always tried to keep return flow from splashing very much.
What you read on this forum is correct. Splashing, combined with adding acid, will decrease TA. When you splash, you can increase the transfer of carbon dioxide from the pool water droplets into the air and this process raises pH without changing alkalinity. Then, when you later add acid to compensate to restore the pH, you lower both pH and alkalinity. So it is the combination of splashing and adding acid that lowers alkalinity, but for practical purposes, you can think of splashing as lowering alkalinity which is what you've heard on this forum.

I believe I do see TA slowly decreasing. I have not taken notes on this, but my recollection is that it slowly decreases over time. I accounted this to the process you describe being accelerated when I add acid. Normally when my pH gets to 7.8 I will add acid to get it back down to 7.4 or so. But even when my TA was 80 (earlier this year), I still saw pH rising at about the same rate. After increasing the TA, I have not noticed pH rising slower.
In the post you linked to (above), you mention adjusting from a pH of 8.0 down to 7.4 once a week and that's a larger change than you are dealing with now which is from 7.8 to 7.4 (or 7.7 to 7.4 since you said a 0.2-0.3 pH change per week) so it does look like the higher TA is helping to reduce the pH bounce somewhat (which is expected). On the other hand, it may also be starting to cause an additional pH increase with outgassing -- this is why the change in alkalinity over time is important to note as this is how to answer what is going on.

Do you notice needing to add more acid per week now than you did when the TA was at 80?

So, are you saying that my TA will continue to decrease until it gets to a stable concentration and then pretty much stay there. And at that point, my pH should only rise about 0.1 units per week? If that's true, that would be great. I will pay more attention to my TA and see if I can notice where it gets to a stable point and if my pH increase slows.
Well, sort of, but not quite. At the recommended pH near 7.5 and TA near 80-120, a pool is always going to be out-of-balance and will want to outgas carbon dioxide. So there will always be some pressure for pH to increase. The idea is to find your pool's ideal sweet spot where the outgas effect is relatively small (TA is low enough) while at the same time you have sufficient buffer to minimize your changes in pH (TA is high enough). That's two competing factors. At the sweet spot, the amount of added acid each week is smaller but without too much of an annoying pH swing.

Very interesting info, but it seems to go against what I have read so far which is to keep my TA around 125.
With the additional info you provided that earlier on you had a TA of 80 and had a large increase in pH, then the advice is not inconsistent. You were clearly in a bad situation with the TA of 80 and you are in a somewhat better situation now with a TA of 125, but perhaps you might be in an even better situation with a different TA (maybe 100 or 110?) but we really haven't figured out what that should be yet.

Thanks again for the interesting info.

Jim

Jim,

Since you still had a very high tendency to increase pH even when the TA was low, I don't think the main problem you are having is outgassing of carbon dioxide. Yes, by setting the TA as high as you have you may have started to introduce a little more extra pH increase as would be seen by a more rapid (but still quite slow) drop in alkalinity and a small increase in the amount of acid you need to add. So perhaps your TA should be dropped a little bit (which will happen slowly over time if you don't add any bicarbonate of soda), but that will not solve the core problem you are having, namely that something is adding a lot of extra base to your pool.

Unless there are other chemicals you are adding to your pool besides chlorine and acid, this extra base being added to your pool must either be coming from the chlorine you are using or from something entering into your pool. One thing you could try, just for a few weeks, is to use a different source of bleach. Even though it's not part of the BBB system, if you go to the pool store and get the more concentrated 12% liquid chlorine, then at least I'm more certain of the amount of base that is in it. Just remember that you only need to add about half as much as you were before. At least this is something to try.

If anyone else has any ideas as to the possible source of this pH increase that isn't significantly affected by TA, please chime in.

Richard

[jereece]

Thanks for the additional info. I have a few comments / questions.

1. I just purchased enough bleach (found it on sale) to last me the rest of this season. I normally close early to mid September. And the only local pool store I have had never heard of using bleach let alone selling it. When I asked from Sodium Hypochlorite, they looked at me like I was an alien. When I told them it was bleach, they still looked confused. So I can't find the higher strength stuff, but I have used at least 3 different brand names of bleach this year and seem to get similar results.

2. I forgot to mention this in my past post, but my CA is in fact 10ppm. I have very, very soft water. Using my Taylor test kit, it only takes one drop to get a color change. I have asked if this is a problem on this board before and even Ben has said for vinyl pools low CA is not a concern. I thought about using some Calcium Hypochlorite for a while to increase it, but I can get bleach cheaper so I have just stuck with bleach.

3. I have not really noticed needing to add acid any less frequent at 120 TA than at 80. However I have not really been keeping records either. So it may be but I just have not taken notice. I still add acid about once a week.

4. Now for a radical question. If having high TA causes an imbalance in the water and if having low TA causes the pH to want to increase less, why not just go with little or no TA? I understand that pH would swing more, but from what I hear you saying it will tend to reach equilibrium and maybe the pH would increase 0.1 units per week. That would not be so bad. So why would I not just have very little or no TA so my pool would be at equilibrium?

Thanks again for the interesting posts.

Jim

[chem geek]

My comments below in bold.

Thanks for the additional info. I have a few comments / questions.

1. I just purchased enough bleach (found it on sale) to last me the rest of this season. I normally close early to mid September. And the only local pool store I have had never heard of using bleach let alone selling it. When I asked from Sodium Hypochlorite, they looked at me like I was an alien. When I told them it was bleach, they still looked confused. So I can't find the higher strength stuff, but I have used at least 3 different brand names of bleach this year and seem to get similar results.
If they sell it at all, it's called liquid chlorine or chlorinating liquid.

2. I forgot to mention this in my past post, but my CA is in fact 10ppm. I have very, very soft water. Using my Taylor test kit, it only takes one drop to get a color change. I have asked if this is a problem on this board before and even Ben has said for vinyl pools low CA is not a concern. I thought about using some Calcium Hypochlorite for a while to increase it, but I can get bleach cheaper so I have just stuck with bleach.
OK, you've got a vinyl pool and that's true you don't need extra calcium, but it does change my calculations in subtle ways, but not too much.

3. I have not really noticed needing to add acid any less frequent at 120 TA than at 80. However I have not really been keeping records either. So it may be but I just have not taken notice. I still add acid about once a week.
What I was asking was the total amount of acid you add per week, but it sounds like that hasn't changed very much so that means that the outgassing of carbon dioxide is probably not very high and not the source of this rising pH problem.

4. Now for a radical question. If having high TA causes an imbalance in the water and if having low TA causes the pH to want to increase less, why not just go with little or no TA? I understand that pH would swing more, but from what I hear you saying it will tend to reach equilibrium and maybe the pH would increase 0.1 units per week. That would not be so bad. So why would I not just have very little or no TA so my pool would be at equilibrium?
If you had a plaster/grout pool then you would need the TA along with CH to prevent corrosion, but since you have a vinyl pool you don't need TA nor CH for that purpose. However, if you had little or no TA, then your pool's pH would swing HUGELY and you'd have to be adding acid every day if not more frequently!

If we assume, based on your numbers, that the additional "hidden" source of increasing pH is equivalent to roughly 1 ounce weight of caustic soda or lye per day, then every day you add chlorine to your pool your pH goes up 0.15 and the chlorine then gets used up during the day and your pH drops back down resulting in a net increase of 0.04 per day. This is at a TA of 120. At a TA of 80, adding chlorine has your pH go up by 0.23 and then the chlorine gets used up and your pH has a net gain of 0.06. At a TA of 10, adding chlorine would make your pH would go up almost 1.1 units! And yes, as the chlorine got used up your pH would drop back down for a net of 0.26, but that's a huge swing and is why you don't want very low TA in your system. Even adding acid every day wouldn't help the situation with a TA of 10. You'd have to add a very small amount of add acid almost every hour to maintain a reasonable pH! If you were willing to add acid every day along with your chlorine (not mixing them, of course), then you could go with a TA as low as 60 which would give a 0.30 increase when adding chlorine and a net gain of 0.07 which you would neutralize with about 3.5 fluid ounces of Muriatic acid per day. I wouldn't go any lower than this 60 TA, but I really don't see much benefit of that since it's more convenient to have the higher TA (say, 100) and add acid less frequently, but it's really up to you.

Thanks again for the interesting posts.

Jim

[jereece]

...every day you add chlorine to your pool your pH goes up 0.15 and the chlorine then gets used up during the day and your pH drops back down resulting in a net increase of 0.04 per day. This is at a TA of 120.

Then something is definetly adding more to pH than the bleach. In 5 years, I have never seen this small of a net increase in pH. I have only used generic brand bleach (5.25 and 6%), but have used a number of different sources. All seem to have similar results. So I don't understand what it could be. I only add bleach and muriatic acid, then maybe adjust alkalinity once around mid-summer with baking soda.

Thanks again for the info.

Jim

[chem geek]

Then something is definetly adding more to pH than the bleach. In 5 years, I have never seen this small of a net increase in pH. I have only used generic brand bleach (5.25 and 6%), but have used a number of different sources. All seem to have similar results. So I don't understand what it could be. I only add bleach and muriatic acid, then maybe adjust alkalinity once around mid-summer with baking soda.

Thanks again for the info.

Jim

.04/day is about .3/week and that seemed to be around what you were seeing. In your post #13 you said that the rise in pH was ".2 to .3 units per week" so aren't we consistent?

Does anyone out there know the pH of bleach? For 12.5% liquid chlorine, the pH of just sodium hypochlorite in water would be 10.6 but the actual pH is about 13 because of sodium hydroxide (caustic soda or lye) that is added since concentrated chlorine breaks down faster at the lower pH. So maybe bleach is more basic than I would have thought and that would explain a strong tendency towards increasing pH for anyone on the BBB system.

Richard

[jereece]

.04/day is about .3/week and that seemed to be around what you were seeing. In your post #13 you said that the rise in pH was ".2 to .3 units per week" so aren't we consistent?

You are correct. I misread and thought you said .04 per week. Sorry, you are correct. That is about right.

The MSDS for 5.25% bleach says the pH is 11.4.

I think what I need to do is check my pH, add bleach and let circulate for an hour, check the pH again then the next day when chlorine concentration has decreased check pH again. It may be difficult seeing any change however with my test kit.

[chem geek]

The MSDS for 5.25% bleach says the pH is 11.4.

Well, if the 5.25% means the weight percentage of sodium hypochlorite then the natural pH would be 10.5 and the amount of base added to make it more stable (if any) is much less than what is in 12.5% liquid chlorine. So that isn't what is going on. Too bad since that would have been an easy answer.

Richard

[CToon]

Since I also suffer from the increase of ph syndrome , I've taken an interest in this ..I dont have the ph swings that some have reported , but I do need to add muriatic acid maybe every 10 days (varies , I havent kept track)

My pool
ph 7.5 normally
ALK 110
vinyl liner

Thinking of the possible cause/contributors , I wonder how much an effect DE is having behind the scene. I dont know the ph of diatomaceous earth , but since its a "chalk" , wouldnt it be alkaline ? and following that couldnt leaching be a contributor ?

just a thought

[chem geek]

Since I also suffer from the increase of ph syndrome , I've taken an interest in this ..I dont have the ph swings that some have reported , but I do need to add muriatic acid maybe every 10 days (varies , I havent kept track)

My pool
ph 7.5 normally
ALK 110
vinyl liner

Thinking of the possible cause/contributors , I wonder how much an effect DE is having behind the scene. I dont know the ph of diatomaceous earth , but since its a "chalk" , wouldnt it be alkaline ? and following that couldnt leaching be a contributor ?

just a thought

That's a possibility, but we'd have to see if there's a trend with the folks who see the consistent pH increase that isn't explained by other known factors like outgassing of carbon dioxide (which one can tell via the alkalinity drop over time, assuming pH is adjusted by adding acid). Are all of these people using DE filters?

Another possibility is the outgassing of chlorine gas, but this would not normally happen fast enough to affect pH except in salt pools -- either SWG pools or pools that have added salt. The concentration of salt (chloride ion) and the concentration of disinfecting chlorine (HOCl) determine the maximum rate of outgassing, though there are the same physical aeration issues as with carbon dioxide except that chlorine escapes more readily since there is virtually no chlorine in the air at all (so it's much further out of equilibrium) However, I don't have any evidence that this is really occurring in pools and it's very difficult to distinguish the difference between chlorine usage from breakdown by sunlight vs. outgassing except for the pH difference (the former is acidic, the latter is basic) and with so many things that can affect pH, well it's a mess to figure out!

You should also think about anything else added to the pool -- any other chemicals at all, including things to tie up metals and prevent staining. I know that non-chlorine shock (MPS) is very acidic, for example.

Then of course, there's the fact that people swim in the pool! I didn't think the pH of sweat was basic and I've seen reports of this rise in pH from people who don't use their pools much, so I don't think that's it.

At some point we may just give up on trying to explain this and just "live with it" and deal with it, but I'm not ready to quit yet!

Richard