Best Guess Table

Is "Ben's Best Guess Table" too conservative for some residential pools? I've seen more than a few people here claim to keep their chlorine at levels significantly lower than the Best Guess Table calls for for a given level of CYA with good results (no algae, no known cases of pathogen transmission through the pool water, etc.). Are they just lucky or might it be safe to keep lower levels of chlorine in certain circumstances? Is Ben's table heavily based on his experience with commercial pools? Is there a safety factor built-in to the table?

Without knowing and controlling for the myriad variables (bather load, accident-prone kid load, leaves and other vegetable matter, sunlight, etc.) that affect chlorine consumption, there would obviously be a good bit of guesswork involved in refining the table at all. However, given all the concern about safe chlorine levels it may be something worthy of further discussion.

I'm not advocating that anyone run lower levels of chlorine than Ben recommends; I'm just suggesting that based on some (admittedly sketchy) anecdotal evidence, some further discussion/inquiry might by in order. Short of that, should the table be treated as more of a starting point or guideline than an absolute? That may even have been Ben's original intent but almost everyone here (me included) now treats it as Gospel instead of as a guide.

(Just some food for thought and discussion; I'm not looking to start an argument.)

I know from experience that with an SWG, you can keep it much lower than the table. My CYA is now at 70 ppm and the chlorine level at 2 ppm without any problems but I have not had a dead cow fall in the pool yet.:D

My bather load is very low, much lower I'm sure than what Ben's guide is estimating, but I still keep my levels based on the guide. Heck, It costs me 12.00 a month in CL, I'm not going to mess with it. If I'm going to get that frugal (And I could, I live in New England) I should pack it up. :)

For acedemic purposes, It may be interesting to find out (I'm not volunteering), but if you get that close to the edge you would probably find it is too varied to have any public value.

Wayne

I would think that given the wide variation of pool conditions (different climates, trees vs. no trees, bugs, rain yada yada yada) these numbers probably work well no matter what. If you tried to build a table that took all of these factors into consideration, it would take a lot of work and it would probably be huge.

I would also think that Ben's table allows for some wiggle room - if you don't get to test for a day or two or have more people in your pool one day or there's a rainstorm, whatever, then it won't cause your pool to go south whereas if you keep it right at the stable point then any little disturbance could put you over the edge.

Also it seems to be one of Ben's goals to make pool care easy for people so rather than have people figure out their minimum chlorine level, here's a universal guide that is reasonable and works. Given that 4 ppm of chlorine is considered acceptable in drinking water, these numbers don't seem like much of a concern.

Peter

I just posted something similar to this question elsewhere today. I have had my pool for 8-9 years and have CYA around 30-40 and chlorine at 1-2ppm and have never had any algea or other problems and the water is always crystal clear. I guess it is like gas mileage, your mileage may vary.

Quote:

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Originally Posted by Wayne LaBanca

My bather load is very low, much lower I'm sure than what Ben's guide is estimating, but I still keep my levels based on the guide. Heck, It costs me 12.00 a month in CL, I'm not going to mess with it. If I'm going to get that frugal (And I could, I live in New England) I should pack it up. :)
Wayne, Cost wasn't my concern. I was really just wondering about the basis for the tabel and whether it might lead to unecessary overchlorination of some pools.

For acedemic purposes, It may be interesting to find out (I'm not volunteering), but if you get that close to the edge you would probably find it is too varied to have any public value.

It would be interesting to collect and analyze some empirical data (e.g. daily chlorine level and CYA, hours of direct sunlight per day, bather loads, microbe counts, algae outbreaks, etc.) from a large number of residential pools and try to find the correlations. It's way over my head from the technical, monetary, and time standpoints. I guess that's why Ben came up with the table.:)

Wayne

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Please don't get me wrong. I think the Best Guess Table is great and I'm confident that the worst it might do is cause some people to overchlorinate their pools somewhat and probably not harmfully. I don't worry very much (really, at all) about the overchlorination issue in my pool, but it's obvious from reading some of the posts on this forum and others that there are plenty of people who worry about it a great deal. If there's a safety factor built into the table maybe people could be more confident in playing around with the levels a little more without too much risk of infections and algae infestations. On the flip side of that, the shock levels in the Table don't seem to have much wiggle room; people who fail to reach those levels, even by a little, often seem to have trouble clearing algae.

For me, the table is for no fuss. Follow it and it is unlikely you will have any problems.

However, for those willing to take some risks with an occasional algae bloom, they can push the limits a bit and see what happens.:eek:

I've noticed that whenever I've let it drift toward the low end of the scale, inevitably thats when I'm most succeptable to problems. Our pool has a cya of 50 , so the range 3-6ppm . I can let it go to around 2 ~ 2.5 without worrying too much , but I cant leave it there for long without CC raising or algea taking off

It may interest some of you to know that one of the forum members, Richard F. (not his forum ID), who has both a strong interest in this topic, and a degree in chemistry, has been investigating it rather intensively over the past year or so. Many of the results he's achieved are extremely technical, but it now looks like we may be able to use some of his work to update the Best Guess Table, early next season.

Ironically, it now looks like the primary changes will be to INCREASE the shock dosages, which are low, if you look at the theoretical HOCl levels achieved. I need to do some liner testing with those high levels before I make those change, however.

Also, please keep in mind, that what I was trying to accomplish with the BGT was a "works for almost everybody / is safe for almost everybody" guide. Inherently, this means creating a guide that is NOT perfectly optimized for each pool, but rather one that is GOOD ENOUGH for almost all pools.

There are several issues to keep in mind.

First, prudent operational conservatism requires the biggest safety margins be maintained adjacent to high risk boundaries, rather than low risk bondaries. Overdosing with chlorine approaches a low risk boundary: the consequences of doing with 6 ppm instead of 3 ppm are almost always trivial. But underdosing with chlorine approaches a high risk boundary. The consequences of maintaining 1 ppm instead of 2 ppm, can be an expensive (in time, money, chemicals and 'stress') episode of algae. It can also result in infection. Consequently, prudent analysis will lead to operational guidelines that err in the direction of overdosing more frequently than in the direction of underdosing.

Second, it is also operational prudent to consider common forms of operator failure, and to set up guidelines, where possible, that minimize the consequences of such failures. With pools, whether home or commercial, 'missed dosing' represents one of the most common forms of operator failure. One possible solution is the use of a feeder. In the past, I've recommended the Rainbow RB-320 as a functional feeder with tolerable 'negatives'. More recently, I've concluded that SWG's are a superior alternative, for those who can afford them. But, high Cl / high CYA represents an operational alternative that is accessible to virtually everyone.

With respect to both issues identified above, I think what I've done, and recommended, largely 'gets it right'. (For this reason, I'd prefer to see less 'how to optimize for low chlorine use' discussion in the general forum sections. I think such discussions tend to lead to pool failure episodes for newbies. Here, in the China Shop, it's fine.)

But, there's a third issue, that of anti-chlorine paranoia. This fear distorts people's perceptions of where the real risks are, causing many (even some of you, apparently) to place a value on low chlorine levels that, in my opinion, is contrary the value that would be attributed as a result of any real systematic analysis of the relative risks and benefits. I've just realized -- actually, when I was posting on the chlorine paranoia yesterday -- that I have not adequately communicated anywhere on my site the information people need to help them make that analysis, at either a 'popular' or a technical level. This is something I need to fix. I'll try to do so this winter.

Meanwhile, I'd encourage some of you to consider what sort of weight should be placed on the benefits of low chlorine (possible reduced costs; reduced suit / liner fading; possible reduced risk of long term effects) versus the costs (low margin of error; increased risk of algae; increased risk of acute infections; increased complication of care guides). I tend to believe that the only substantial realized benefit to optimized low chlorine is what might be called 'tinkerer's satisfaction'. By this, I mean the satisfaction gained by someone who tunes up their PC, and then runs a test to validate that it now benchmarks at 18,700 whatevers instead of the 16,980 whatevers it was running before. The functional benefit of this sort of improvement is virtually nil, but the psychic satisfaction is high.

Please understand that I see nothing wrong with pursuing 'tinkerer's satisfaction': I've done so many times myself. But, the reality is such optimization is NOT what most newbies here need. Instead, they need help in achieving 'good-enough', reliable, and trouble free operation. They can (as some of you have) learn to 'tinker' later, once they've gotten the basics down.

I'd ask all of y'all here to consider adopting such a point of view, when you post in the general forum . . . for the sake of people who just want their pool to work.

Thanks,

Ben Powell
"PoolDoc"

Ben
If I may put my 2 cents in here.
I also posted in the other forum you mentioned. Most pathogens can live in non chlorinated water. The levels of suggested chlorine allow for rapid kill times. This becomes important if an infected person enters your pool to prevent the spread of the infection. It is even more important of you have a person with a lower immunity. Children under the age of 3 to 5 are at higher risk due to an undeveloped immune system. Some thing that will give an adult a good case of gut cramps could in essence kill a child.
With the emergence of antibiotic resistant pathogens we are now seeing in the lab total kill of these pathogens is not optional.

I am not as concerned about the growth of algae in my pool. The appearance is a small part of the reason I feel the levels of chlorine should be kept levels mentioned in the best guess chart. I have said it once and will again if you have algae it’s the least of your problems. You may have a killer in your pool as well hiding in the algae.

I tend to weigh all decisions concerning the health of the persons in my house very carefully. I looked at the risk of exposure to chlorine levels in the best guess chart verses exposure to the pathogens that can be found in the pool environment. I feel that the exposure to chlorine levels given the best guess chart are lower risk than exposure to pathogens.

Bottom line is that I will tinker with my computer, I will tinker with my truck, I will even tinker with my toys:D , but I will not tinker with my family’s health.
Steve