Ben Powell and his "high pH pool" theory

[Titanium]

Hello,

Like most of you, I started out on Ben Powell's Pool Forum. Great site and I have learned a lot. Shame about Ben going AWOL, though.

One intriguing tidbit that I found somewhere on Ben's site is his assertation that a running a high pH pool has certain advantages. He was going to write up a white paper on this subject, but alas, this has fallen by the wayside.

Does anyone with a decent chemistry background have any clue to what Ben was hinting at?

Thanks!

Titanium

 

[Guest]

The 'high pH pool' was actually started by Jock Hamilton of United Chemical, along with the Hamilton Index for water balancing. Ben said in a post a year or two back that he didn't think it really offered any true advantage except in helping United Chemicals mostly bromine based products work better.

 

[JasonLion]

I suspect that part of what was going on was that people didn't understand about CO2 outgassing. By raising the PH they reduced CO2 outgassing which meant fewer chemical additions trying to control PH. I don't have any solid evidence other than the way Ben talked about it, saying more stable PH levels was one of the big advantages.

 

[chem geek]

That's my take on it as well. At higher pH (and lower TA), the outgassing is slower so the tendency of the pH to rise is less. The downside is that the higher pH is less ideal for the eyes. I assume other water chemistry parameters are kept in balance to maintain calcium carbonate saturation (so lower TA and/or CH to go along with the higher pH). The other downside is the lower effectiveness of chlorine at higher pH, though that is less of an issue when there is CYA in the water (though is still a factor) and can be mitigated by somewhat higher FC levels.

 

[KurtV]

Here's the article. You should read the whole thing, but this is the money quote from a pros and cons standpoint:

"+
Operating your pool at high pH will often, but not always produce these benefits:

* reduced consumption of sodium bicarbonate (alkalinity)
* reduced or eliminated consumption of calcium chloride (calcium hardness)
* reduced or eliminated consumption of acids (pH minus)
* reduced eye and skin irritation
* reduced formation of irritating chloramines (combined chlorine)
* reduced 'chlorine' smell
* reduced problems following 'shocking' or 'breakpoint chlorination'
* increase the effectiveness of ammonia based chlorine 'enhancement'.

I suspect (with some evidence) high pH will also

* reduce halogenated volatile sanitation byproducts (primarily an issue with indoor pools)
* reduce corrosion of indoor pool enclosures
* reduce swimmer irritation from high chlorine levels
* improve control of biofilm forming organisms, e.g. psuedomonas aeruginosa and 'mustard algae'

-
However, high pH often will also tend to

* precipitate metals in pool water, such as copper, iron or manganese
* lower the measured ORP for a given DPD chlorine level (only important if you have and ORP controller on your pool)
* increase the time required to kill a particular pathogen with a given DPD chlorine level (eg, the Ct value for a given DPD chlorine level)
* make broadcasting of calcium hypochlorite (HTH) to your pool problematic.
* increase scaling if your calcium and alkalinity are too high. "

Interestingly, he touches on the subject of using borates as a pH buffer.

 

[Titanium]

Thanks for all of your replies. The previous post contains a link to the very article of Ben's that I was referring to.

I'm still trying to get my head around the notion that Ben only used 50 pounds of acid - over five years - for a 300,000 gallon pool.

Since I add roughly 2 gallons per week of 10% liquid chlorine from Orchard Supply Hardware, my pH tends to rise over time. I started adding acid once my pH rose to 7.8 Is Ben implying that the rise in pH will STOP at some point despite the continual addition of liquid chlorine?

The benefits that Ben cites of decreased consumption of sodium bicarbonate and calcium chloride do not seem of much benefit in my situation in that I have never seen the alkinity level or calcium hardness levels ever change.

Titanium

 

[JasonLion]

Liquid chlorine does not cause the PH to rise. The two common causes for PH rise are plaster less than one year old and high total alkalinity combined with aeration. If you post a full set of numbers we might be able to suggest something that will help reduce the rate or eliminate your PH increase.

 

[chem geek]

Yes, the reason that the pH rises in most pools is that pools at a pH near 7.5 are intentionally over-carbonated, just like a carbonated beverage (though obviously not AS carbonated). This is done to provide a pH buffer (the carbonate buffering system) and to add carbonates to the water which along with calcium added to the water saturate the water with calcium carbonate to prevent the dissolving of plaster. The outgassing of the excess carbon dioxide in the water relative to the air causes the pH to rise over time and requires acid to be added to lower the pH (and the TA gets lower over time as well so sodium bicarbonate also needs to be added).

There is an equilibrium amount of carbon dioxide in the water and the air and this corresponds to the following TA and pH levels, assuming 30 ppm CYA (since CYA is a component of TA). Essentially, the following combinations of pH and TA, with 30 ppm CYA, all result in identical amounts of carbonic acid (dissolved carbon dioxide) in the water and this amount is the equilibrium amount with the carbon dioxide in the air so there is no net ougtassing and no pH rise.

pH .... TA ..... Saturation Index (with CH=300)
--- .... --- ..... -------------------
7.0 ... 10.5 ........ -1.94
7.5 ... 19 ........... -0.93
8.0 ... 40 ........... +0.06

So you can see that by raising the pH and having a low TA you can still have the saturation index near 0 so that the water is saturated with calcium carbonate as is needed for plaster pools, but there can be no carbon dioxide outgassing and therefore no pH rise from it. In practice, you can have higher TA and have so little outgassing that it won't be noticeable. Ben's comments about not doing the higher pH in a higher CH pool imply that the TA is not normally lowered. A TA of 80 with a pH of 8.0 would have a saturation index of +0.44 which is slightly scaling (may not show up until +0.7 or more) and would only have 1.4 times as much carbon dioxide in the water "extra" above its equilibrium amount (so 2.4 times its normal amount) which isn't that much higher.

I disagree with some of the benefits that Ben listed. I don't understand why there would normally be "consumption of calcium chloride" in standard pH pools. The reduction in needed bicarbonate and acid makes perfect sense. The reduced eye and skin irritation doesn't make sense to me and I would expect MORE eye irritation at the higher pH since the average of human tears is 7.5, not 8.0, but perhaps this isn't a big difference. Chloramine formation is somewhat reduced, but other disinfection by-products are increased -- different ones have different pH points where they are produced in greater quantities. Chlorine "smell" would be chloramines so that makes sense. Lower metal corrosion makes sense. Not sure about biofilms.

I think the only serious downsides are the metal precipitation and possible eye irritation so this isn't bad and not adding metals is usually controllable (unless fill water is full of metals -- but metal sequestrants can be used). The reduced chlorine effectiveness just means, in the presence of 30 ppm CYA, that one needs to increase the FC level from 3.5 (at pH 7.5) to 4.0 (at pH 8.0).

See this thread for an extreme example of running at very low TA that eliminated the pH rise problem. It is not necessary to run at high pH, but for a plaster pool one might need to increase the CH to maintain calcium carbonate saturation. Quite a few users have tried lowering TA to reduce the tendency of the pH to rise and it has worked successfully for almost all of them. For SWG users, using 30-50 ppm Borates in the pool also helped as described in this thread.

Richard

 

[tppflorida]

As a pool technician (which doesn't mean much in most cases, but I really try to educate myself), I can tell you that from a customer point of view, a high ph actually causes less irritation to the skin and eyes than does a lower ph.

Having said that, in most cases where this has been noticed is in situations where some people have a bad reaction to lower ph levels. Even a ph of 7.6 irritates their skin, and even more so, if the water is heated. In those situations, I have used the Hamilton Index for their water chemistry and the irritation of skin and eyes has been resolved.

So while I may not have scientific data to back up my claim, I do have some customers that swear by the only change I made... and that was to their ph levels. Just my contribution to the group :-D

Michael

 

[JohnT]

As a pool technician (which doesn't mean much in most cases, but I really try to educate myself), I can tell you that from a customer point of view, a high ph actually causes less irritation to the skin and eyes than does a lower ph.

Michael, Ben's article mentions a study that concludes that a pH about 8 is easiest on the eyes, so there is some science to back up your experience. Don't belittle your own real-world experience. Often you know more than you think you know, and when you read the science, it makes more sense than either would alone. We are always glad to have pros of all flavors here for their input.

Switching to Moderator mode since I'm already posting, and addressing all posters in the thread: Nobody has done this yet, but please be careful about quoting from Ben's article. It's his creation and his property. Snippets and links are, IMO, fine, but Ben and Sean have the final say there.

 

[chem geek]

It may very well be that water with a pH of 8 is easiest on the eyes, but the pH of human tears is closer to 7.5 as described in this link or this link which are the same thing ([EDIT] there is also this link and this link). The main difference between pool water and human tears is the salinity (salt) and that is the biggest complaint (at normal pH) in terms of feeling in the eyes because exposure to water that is less salty than the 9000 ppm of human tears will tend to flow into the eye increasing pressure (via osmotic pressure).

Richard

 

[SeanB]

John, it's my understanding that in most cases, like on a public forum, you do not have to have permission to quote someone since that person is basically putting it out in the public domain when they post.

However, if you are quoting someone verbatim, or copying an article it's always a good idea to credit the source.

Thanks,
Sean

 

[KurtV]

The "fair use doctrine" is applicable here. You always need to attribute properly (e.g. provide a link to the source); assuming you do that, it's almost certainly permissible to post excerpts of articles and forum posts on this and other forums.