You may have seen recent press releases about the IPSSA-funded study by the "National Pool Industry Research Center" at Cal-Poly San Luis Obisbo. The study was to determine whether or not salt generator pools can be serviced with once-a-week service visits.
According to the Pool and Spa News report, the conclusion of the study is "'With a once-a-week service visit, we found that the water chemistry of a salt-chlorinated pool will not stay within the parameters that IPSSA considers acceptable,' said Lance Sada, IPSSA’s liaison to the NPIRC."
More details are available at IPSSA's website.
Is this your experience? How do you feel about this conclusion?
Replies
In this salt study to determine if once a week treatments are sufficient, there was no examination of the one pool to determine whether the plaster surface etched, or was scaled. In prior experiments conducted by the NPIRC, an inspection of the plaster on all pools was performed. Why not for this study? Also, for this particular study, a report on water cloudiness and algae could have been performed. Even the IPSSA liaison stated bather comfort and pool equipment protection was an intended purpose of the study (Dec 2010 IPSSAN). But no examination of any kind was performed. This unfortunately allowed for a premature and incomplete conclusion.
The study's protocol also says that "an additional object of this Salt Pool (Phase 1) study is to identify, any service or procedural changes which could be employed to ameliorate the (pH) deviations (the rising of the pH) in the water chemistry which occur during this weekly interval between service calls."
It appears that this study never identified, or tried to control or slow down the rising of the pH because the TA was never lowered to 80 ppm, and interestingly, was not suggested in their recommendations for future studies. Most chemists know that lowering the TA helps prevent the pH from rising as high and as quickly.
Did you know that the scientists at the NPIRC already had the opinion four years ago, that service techs could not keep pool water properly balanced (even in non-salt pools) with once a week visits? (The IPSSAN November 2006 p. 20) And no, there was no study then that had proved that claim – only their own inability to do so.
It has been acknowledged that alkalinity “may not have been taken into account” and/or that the “salt” study is incomplete with more protocols being considered. Therefore, it is irresponsible and wrong to CONCLUDE and ANNOUNCE that salt pools cannot be maintained properly with once a week visits. This announcement hurts service techs, and will enable and encourage some plasterers to blame service techs for what may actually be plastering-caused defects and discolorations. Plasterers can do this by simply showing the homeowner the printed “Headlines” in the press.
This is not the first time that flawed studies and conclusions have been announced by the NPIRC and NPC and used against service techs. The first two phases by the NPIRC were flawed and inconclusive, yet it was announced that water chemistry is the primary cause of certain plaster defects (some of which were incorrect conclusions), and plastering consultants have used this against service techs.
It is great to have so many service techs speak out on the obvious mistakes with the study (as seen in P&SN, IPSSAN, and PGN online sites). It is disappointing that there has been some criticism of the messengers. But plaster apologists should not be allowed to use this “study” as a weapon over a service tech’s head.
This is what happens when people have an agenda rather than looking at known science for answers. Well, at least they were mature enough to admit their mistake and plan to try again.
For some pools, they may need to get the TA even lower below 80 ppm (say, to 70 ppm), target a higher pH of 7.7 to 7.8 ppm, and use close to 80 ppm CYA if the pool is in direct sunlight in which case the FC target should be 4 ppm. The CH may need to be raised somewhat (more like 400-500 ppm) to have a near-zero saturation index though one usually targets a slightly negative index to help prevent scaling in the salt cell.
Another technique that can be used in conjunction with the above is to use 50 ppm Borates in the pool which acts as an additional pH buffer and also helps inhibit nascent algae growth. After all of this is done, the SWG on-time can usually be lowered which, along with the lower TA and higher pH target, helps reduce the rate of pH rise. See Total Alkalinity (TA) and pH Effects for a more technical discussion.
IPSSA finally responds to salt study critiques. Interesting read is more in the comment section.
http://www.poolspanews.com/2011/031/031n_ipssa.html
Scott Heusser said:
I share Kim’s and Richard’s concerns about the lack of ingenuity at the NPIRC. Further, I am embarrassed by their apparent incompetence. That is why I instigated this forum question, wondering if others shared my feelings. As a point of order, and in the nicest way possible, please focus discussion in this specific forum discussion on the research report I linked. A forum could separately be instigated to discuss tangential topics (such as a general or specific treatment of the pH effect of a particular chlorinating system).
onBalance, composed of Kim, Doug Latta and myself, has already pointed out that in the first two phases of the NPIRC research (the only ones where actual chemical data are available) the research personnel failed to maintain the test pool target chemistry within the target ranges… with often over 50% of the given readings out of range. Yet they make conclusions on water chemistry-caused phenomena based on those significantly out-of-range experiments. Here is an interesting fact: the NPIRC has shown in its earlier research publications that they were incapable of maintaining water within industry standards, even when treating the water more than once per week.
Again in this experiment, they were incapable of maintaining a salt pool within range when restricting themselves to once-a-week treatments (see the above link to the IPSSA published data). Should this be a surprise?
What makes the situation worse is that the specific parameter of concern was pH. The conclusion was that pH rises too quickly in a salt pool to wait a week before lowering it again. Since pH increase is significantly influenced by the concentration and content of the buffer (the TA level and the type of alkalinity present), alkalinity levels are of primary concern in the setup and follow-through of the project. So what did they do?
First, they designed the experiment with a target TA that was too high. The APSP ideal standard for TA in a base-sanitized pool is 80-100 ppm. This is because a lower starting point for TA (as compared to the ideal of 100 to 120 for acid-based sanitizers) allows for upward mobility while still staying in the target range. But the NPIRC target was 100 +/- 20 ppm. So from the get-go, they were willing to accept TA readings as much as 20 ppm higher than what the APSP considers optimal for a salt pool.
Then they ran the experiment… and failed to keep the TA in the targeted range. A look at the readings in the linked data shows that the TA was commonly over 120 ppm.
Now, if they had a problem with an unrelated parameter, they could perhaps be given a pass. However, in this specific instance, maintaining a TA of 120-150 ppm directly biases the water toward higher pH! So their failure directly enhanced the result of the experiment!
This all doesn’t take into consideration the additional issues, such as that fact that there are known methods for buffering pH, and even that there are known alterations of common operating chemistry that allow for higher pH levels to be acceptable (i.e., non-scale forming and yet still sufficiently sanitizing) in pools.
So again – how does this all make you feel? Either we are misunderstanding the setup and results of the test, or the NPIRC has once again taken donations and returned bogus conclusions.
Sorry I wasn't clear in my post. I was not saying that the type of chlorine source doesn't matter with regards to the effect on pH. What I was saying was that people often neglect to consider that the chlorine usage/consumption is acidic. Except for the "excess lye" in some hypochlorite sources of chlorine, this makes such hypochlorite sources (and SWG systems) net pH neutral in terms of the chlorine. It also makes Dichlor net acidic, not near pH neutral, and it makes Trichlor even more acidic than it is upon addition.
In your residential pools using hypochlorite sources of chlorine, if you significantly lowered the TA, to even 50 ppm, you would find that the pH would actually rise much more slowly or even approach stability, unless you've got other sources of rising pH such as curing plaster. I'm not recommending such a low TA as it usually doesn't need to get that low for most pools, but even a low TA is over-carbonated water that will have the pH more likely to rise. In residential spas using Dichlor-then-bleach, the TA needs to be lowered to at least as low as 50 ppm for the pH to be fairly stable when using bleach. Borates can be used as a supplemental buffering system to allow for lower TA and the CH can be raised to keep the saturation index balanced for plaster pools.
The following is the equilibrium pH where carbon dioxide outgassing will completely stop at each TA level with no CYA (so the TA is the same as carbonate alkalinity):
TA ..... pH(eq)
120 ..... 8.6
100 ..... 8.5
80 ....... 8.4
50 ....... 8.2
30 ....... 8.0
20 ....... 7.8
10 ....... 7.5
Fortunately, one does not have to get the TA as low as 10 or 20 ppm to have the carbon dioxide outgassing be slow enough to have the pH be effectively stable, but the point is that 80 ppm can still be too high, especially when there is reasonable aeration of the water. Experiments by Wojtowicz showed that the rate of carbon dioxide outgassing varied as the square of the TA so it can drop off fairly rapidly as one lowers the TA.
In this post, you can see how the amount of acid per time period drops as the TA is lowered from 100 to 60 and how in this post the same pool owner with the pool now at 50 ppm saw the pH only going from 7.3 to 7.4 over 4 days without having to add any acid. When he started, with the TA at 100 ppm, he was adding about 2 cups of acid every day. This experience has been repeated over and over again (see this post for another extreme example), though as I wrote earlier, with SWG pools there are other factors contributing to rising pH so lowering the TA only addresses one of those factors.
Richard raises a valid point in his first post of this forum. A low TA (about 70 ppm) helps to slow down the pH from rising so fast in comparison to a TA of 120 ppm. This has long been understood and is common knowledge by most chemists and many service techs across the country.
Yet, if you review the protocol in the NPIRC report, they set the TA parameter at 100 (+/- 20) ppm. Why didn’t the NPIRC set the TA at 70 ppm where the pH would be less likely to increase so rapidly? It is no wonder that the pH rose quickly in their test pool.
Furthermore, as Richard stated, there are other ways to lessen the natural rising of pH. Raising the CYA can help, and adding borax can also help maintain a more stable pH. Indeed, the pool service company I own has adding borax to pools since the early 1960s. Besides helping to prevent algae formation, we used it as a pH buffer and to prevent calcium carbonate formation when the pH is on the high side. The use of borax in pools has been known industry-wide now for many years.
There are other known variables that can help maintain the proper water chemistry in a SWG pool, and should have been considered by the NPIRC study (and I am not talking about an acid auto feed system). So the question is, why didn’t the NPIRC incorporate principles and practices known throughout our industry that would have helped prevent the pH from rising too quickly? Why did they simply announce to pool techs (and to the rest of the industry) that it is impossible to properly maintain a SWG pool with weekly visits?
And are we going to simply shrug our collective shoulders and accept the conclusion (that we are incapable of maintaining a given pool on a weekly service visit basis) when the best chemical practices available are not being applied to the scenario?
Richard,
i completely understand the issue in keeping the TA at the proper levels and the ph "bounce" that you will get with the wrong levels. However i will tend to disagree with you regarding the fact that the type of chlorine will not affect the level of pH. Our company services @250 pools a week, both commercial and residential, with all different types of chlorination systems. Pools that operate on trichlor pucks will typically need pH increaser as their pH tends to be on the lower side of the scale, while those that operate on liquid chlorine or SWG are typically on the higher end and require acid to lower the pH. this occurs throughout the entire scale of Alkalinity, although we are typically keeping them around 80 to 90ppm.
Richard A. Falk said:
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