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Thread: Interesting article on CYA/FC levels...

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    Interesting article on CYA/FC levels...

    I was looking for something else, and found this - seems to be contrary to the CYA chart...

    http://www.ncbi.nlm.nih.gov/pmc/article ... 3-0245.pdf

    - Jeff
    ~45Kg Pool with attached Spa, NSP-72 DE, Minmax 400 Heater, Tahoe Blue Pebbletech, Jandy SWG via Aqualink RS-8, The Pool Cleaner (black)
    Pumps: X3 Hybrid Pump (switches to SPA), 2HP Spa (additional, when SPA is on), and a 1HP For Waterfall
    8, 4x12 Solar Panels on the roof of the pool-house (~12' up)
    CAPTAIN JAMES T. KIRK: "I'M SORRY. I CAN'T HEAR YOU OVER THE SOUND OF HOW AWESOME I AM" (Thanks to TFP!)

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    Re: Interesting article on CYA/FC levels...

    Jeff,

    That is one of the articles I mention in the "Chlorine/CYA Relationship" section of the Certified Pool Operator (CPO) training -- what is not taught post. Specifically, I wrote the following:

    I and others who are technically oriented on this forum have pored through the scientific literature and found that the chlorine/CYA relationship holds extremely well in almost every case, be it for killing of bacteria (here, here, here, here), inactivation of viruses (here), protozoan oocysts (here, here), inhibition of algae growth (this paper claimed no correlation, but real pools say otherwise; Sommerfeld never wrote back to me when I questioned this), and oxidation of ammonia and organics (here) as well as correlation with ORP (see this post and this paper). I've also gone through field study data where the industry makes claims that only Free Chlorine (FC) matters in "real pools" yet I saw that bacteria are killed so easily that you can't even draw that conclusion from such studies and that hypochlorous acid (HOCl) is at least as good a predictor though they never looked at that correlation nor the FC/CYA ratio as a proxy (see this thread).
    As you can see, I wrote that the paper claimed no correlation between algae kill rates and CYA. It is the only peer-reviewed scientific paper I have found that is inconsistent with the FC/CYA relationship and furthermore that paper is inconsistent with what is seen in tens of thousands of pools. I've speculated in the past at what might have happened with the experiments in that paper such as the "algal inoculum" perhaps contaminating the experiment. For example, if such material contained ammonia, then that would quickly react with chlorine to form monochloramine that would be independent of CYA level (since monochloramine does not bind to CYA). The paper does describe how the culture medium did have a chlorine demand (1.21 ppm FC for 500 ml volume) and that they met that demand by adding chlorine, waiting 24 hours, then exposing the medium to sunlight to remove chlorine. Of course, the sunlight won't remove many combined chlorine that would be slow to oxidize (such as chlorourea, if urea was present), but I would presume that IF they added sufficient chlorine, then ammonia would get fully oxidized.

    They then say they added stabilizer to the chlorine demand-free culture medium and then added 1 ml of chlorine and then 1 ml of algal inoculum. They earlier described how algae cultures were maintained in exponential growth phase and that they had daily replacement of the culture with fresh medium, but obviously they didn't create chlorine demand-free medium during this process (otherwise that would kill off the algae) and they describe this medium before they talk about the culture medium that they created to be chlorine demand-free. So it is possible that while the culture medium they used for adding CYA and chlorine was made chlorine demand-free since they say that explicitly, the algal inoculum may not have been chlorine demand-free (beyond the algae, of course). Obviously, they could have used the same chlorine demand-free culture medium in both steps (i.e. to grow the algae for the inoculum and also for the culture medium of the experiment adding chlorine and CYA with algae), but they didn't explicitly say that they did this. Yes, it's a stretch, but would explain the results seen. The higher chlorine levels would kill off the algae because it would create sufficient monochloramine to not get used up killing algae while the lower chlorine levels would not create sufficient amounts of monochloramine so enough algae would be able to survive, but in any event the kill times would be independent of CYA level.

    In fact, one of the bacterial kill papers I linked to earlier, namely this one, shows in Figure 1 precisely the effect I am talking about. Note how in 1A the kill time is significantly affected by the CYA level where the time is very fast with no CYA and much slower with CYA, but in 1B the kill times are fairly independent of CYA level. 1A is chlorine without any ammonia present while 1B has ammonia in sufficient quantity to produce monochloramine in all cases (0.1 mg/L NH4-N with 0.5 mg/L FC completely produces monochloramine -- the higher ammonia levels have excess ammonia and may have slower kill times by providing a nitrogenous nutrient of ammonia competing with the monochloramine that kills).

    I should note that there is an acknowledgement at the end of the Sommerfeld/Adamson paper to Olin Corporation who provided grant support for the research. Olin Corporation was one of the key manufacturers for Cyanuric Acid and chlorinated isocyanurates (you can search for many patents associated with them).

    Arch Chemicals, who make Cal-Hypo that competes with chlorinated isocyanurates (e.g. Trichlor and Dichlor), has an article on Overstabilization and another on Cyanuric Acid and Overstabilization both showing increased algae growth rates at higher CYA levels keeping FC levels constant (i.e. lower FC/CYA ratios). However, these are not peer-reviewed studies published in respected scientific journals and the latter study which describes plaster deterioration and CYA drop at high CYA levels was not able to be reproduced by OnBalance though they do see higher algae growth rates at lower FC/CYA ratios and the pool service Pool Chlor uses such chlorine/CYA principles in maintaining over a thousand pools.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Interesting article on CYA/FC levels...

    Thank you for the info - I was looking across the web for something else and ran across this, and was interested in your take.

    I also manage CYA in all of our pools, with a goal of starting the season around ~30ppm of CYA - with a max of ~60PPM at the end of the season. All pools are also raised to 50ppm Borates (via Boric Acid - cheaper and easier than Borax) at the beginning of the season (or when the customer signs on for service).

    A few pools we get it is difficult to get the owner to fork over money for a partial D&F or purchase the Borate treatment. One pool we have is over 100ppm and the customer refused Borates (via Boric Acid) - we generally have been keeping it higher in FC, and using some Sodium Bromide (a discussion for another thread - I know several people's opinion on it) when necessary. A few other pools, particularly those with OLD plaster, have reoccurring bouts of MA - even after we "kill" it.

    I would be interested in your take on the Pool Chlor principals and what you know - from what I see on their website, it appears that they have some mystical recipe that sounds like CYA management, possibly borates, and UV (???)?.

    Thanks for the response.

    - Jeff
    ~45Kg Pool with attached Spa, NSP-72 DE, Minmax 400 Heater, Tahoe Blue Pebbletech, Jandy SWG via Aqualink RS-8, The Pool Cleaner (black)
    Pumps: X3 Hybrid Pump (switches to SPA), 2HP Spa (additional, when SPA is on), and a 1HP For Waterfall
    8, 4x12 Solar Panels on the roof of the pool-house (~12' up)
    CAPTAIN JAMES T. KIRK: "I'M SORRY. I CAN'T HEAR YOU OVER THE SOUND OF HOW AWESOME I AM" (Thanks to TFP!)

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    Re: Interesting article on CYA/FC levels...

    Also, Do you know of any papers with data showing consumption of FC vs. hours of sunlight vs. CYA?

    Thanks.
    ~45Kg Pool with attached Spa, NSP-72 DE, Minmax 400 Heater, Tahoe Blue Pebbletech, Jandy SWG via Aqualink RS-8, The Pool Cleaner (black)
    Pumps: X3 Hybrid Pump (switches to SPA), 2HP Spa (additional, when SPA is on), and a 1HP For Waterfall
    8, 4x12 Solar Panels on the roof of the pool-house (~12' up)
    CAPTAIN JAMES T. KIRK: "I'M SORRY. I CAN'T HEAR YOU OVER THE SOUND OF HOW AWESOME I AM" (Thanks to TFP!)

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    Re: Interesting article on CYA/FC levels...

    The basic approach of companies like Pool Chlor that use gas chlorine, sodium hypochlorite, or both, and that only do once-a-week visits is to use a high CYA level such as 100 ppm to minimize the loss of chlorine in sunlight and to raise the FC level high to around 14 ppm so that it will roughly last the week until the next visit. In the hot desert climates they service, the daily chlorine loss is around 15% so that after 7 days the FC drops to around 4.5 ppm (lower, if the pool is used frequently). This allows them to visit their client's pools once a week. The use of 50 ppm Borates is often done as well, but it's the FC/CYA ratio in the 5-15% range that is the main key to preventing algae growth (the borates act more as insurance and as a pH buffer). Even if nascent algae starts in the day or two before a visit, it gets killed off by the higher chlorine level when the chlorine is added.

    Note that a once a week approach can lead to larger pH swings so that is one reason why additional pH buffering from Borates and/or a somewhat higher TA level are used. The use of a mix of gas chlorine with sodium hypochorite also lets one add the chlorine in a way that doesn't have the pH change as much upon addition (chlorine gas is very acidic while hypochlorite is basic upon addition). The higher TA can keep the pH more stable through the week with the pH rise from outgassing compensating for the drop in pH from chlorine usage/consumption. Replenishing the lost TA would be done as needed during the weekly visit.

    Basically, they are just doing a similar, though a bit more sophisticated, managed maintenance that you are doing, but you take the approach of a more moderate CYA level and twice-a-week visits. Your in-between visit can, of course, be a very fast one that just measures the water chemistry and adds chlorine while the other (weekly) visit can be longer doing brushing of pool surfaces, for example. Your method is closer to what is done here at TFP by individual pool owners and provides a more consistent chlorine level. The pool owners with the weekly pool service peak at 14 ppm FC with 100 ppm CYA normally don't notice it, but for those who are most sensitive to chlorine what you are doing is less likely to be noticeable.

    The pool service where I live (that I don't use, but I go to their store to buy 12.5% chlorinating liquid) services thousands of pools in the area and they generally use Trichlor tabs/pucks in either floating feeders or inline chlorinators, but they target 4.5 ppm FC and they sometimes shock the pool with chlorinating liquid during their weekly visit if there is visible algae or higher chlorine demand. They do not know about nor follow the FC/CYA relationship so do not change their target as the CYA level changes. When the CYA level reaches 100 ppm, they do partial drain/refill to lower the CYA level. With many pools using cartridge filters due to water restrictions in our area, they usually need to do this partial drain/refill at least once during a season. Winter rains dilute the water further in preparation for the start of the next season.

    As for papers showing chlorine loss vs CYA level, there are several and none of them seem to tie well to what we see in real pools in details, though they do show consistent characteristics. This paper from Wojtowicz shows information in Figure 1 from Monsanto that shows that even low levels of CYA such as 25 ppm make a huge difference compared to no CYA, but then they show that higher CYA to 50 ppm is a small difference and to 100 ppm and even smaller improvement. This is inconsistent with what we have seen in real pools and confirmed by Mark's experiments that showed a greater than proportional increase in CYA protection going from 45 ppm to 80 ppm and also we have seen much higher losses when the CYA level is too low (30 ppm or lower, for example). The other information in the Wojtowicz paper shows that chlorine oxidation of CYA gives a chlorine demand, but it is higher than we see in most real pools (but then Wojtowicz used 138 ppm CYA for his tests and the loss rate would be proportional to the product of CYA and hypochlorite described in this paper). See also this paper of Wojtowicz in Figures 7 and 8 showing the loss of CYA over months from oxidation by hypochlorite where the "p = 0.01" curve does seem to be close to what is seen in most pools while the "p = 0.02" curve has only been reported in a much smaller number of pools on this forum.

    As for your question of chlorine loss from sunlight, there are many different factors for chlorine loss so there isn't a single set of numbers to give you that would be precise. There is some chlorine loss from oxidation of pool cleaner bags, pool covers, cartridge filter material, metal and equipment that is all independent of bather load, but whose rate is related to temperature. The oxidation of organics in the pool including blown-in pollen, leaves and other material is also a factor as is bather waste (mostly urea, ammonia, creatinine and amino acids from sweat and urine). We don't have clear data on the temperature dependence, but it seems to be roughly a doubling of rate for every 13ºF so cooler pools have a lower base chlorine demand. We know that bather load is a relatively minor factor requiring around 4 grams of chlorine for every person-hour in a pool (competitive swimmers require roughly double this amount) so 2 person-hours in 15,000 gallons is 0.14 ppm FC. So all of these sources of chlorine demand need to be subtracted out and what is left is that lost from sunlight. You can roughly figure this out by subtracting out a 12-hour overnight chlorine loss from a 12-hour daytime chlorine loss and then double to get a 24-hour average sunlight loss. The following is a very rough estimate of the % FC loss per day at different CYA levels all assuming that the same FC/CYA ratio is maintained (but chlorine added just once for the day) and in a strong sunny environment at peak summer:

    CYA ... % FC Loss ... FC Loss at 10% FC/CYA Start ... FC End
    100 .... 15 ................... 1.5 .................................... 8.5 (8.5%) OK
    80 ...... 20 ................... 1.6 .................................... 6.4 (8.0%) OK
    50 ...... 40 ................... 2.0 .................................... 3.0 (6.0%) on the edge
    30 ...... 60 ................... 1.8 .................................... 1.2 (4.0%) TOO LOW
    20 ...... 75 ................... 1.5 .................................... 0.5 (2.5%) TOO LOW
    0 ........ 99+ ................. N/A

    The above is why those in the sunniest climates usually use higher CYA levels and have to add chlorine more frequently (also, the temperature of their pools tends to be higher which adds to daily chlorine losses). Now we have people with lower CYA levels that are able to maintain their pools, but in many cases they are in part shade or have pool covers that reduce some of the chlorine loss. Note that part of the reason for the higher % losses at lower CYA levels is from the absolute chlorine loss that is independent of the CYA level shown above because it is based on the active chlorine level which is constant since the same FC/CYA ratio is being used. So 0.5 to 0.7 ppm FC per day might be a daily non-sunlight loss and would make the loss from sunlight alone at 30 ppm CYA more like 40%.

    Given that you start your pools with only 30 ppm CYA, what kind of losses in chlorine are you seeing? Are these uncovered pools exposed to strong sunlight all day during the summer? I'm surprised you are able to manage those pools only twice a week at that low CYA level. Also, for the pools with old plaster that get mustard algae, do these pools have borates or are these pools whose customers refuse to pay for borates? I'm just curious if the borates help against mustard algae at all -- we know they help against green algae.

    It would be great to get some real experimental data to isolate the various loss rates -- improving the loss rate data for hypochlorite oxidation of CYA, for the general temperature dependence of chlorine oxidation of various substances normally found in the pool, and for chlorine loss from the UV in sunlight at different CYA levels and water depths (since there is a CYA shielding effect separate from the protection by binding to chlorine). In particular, getting a better understanding of how light interacts with chlorine bound to CYA would help explain the loss rates that are higher than would be predicted by loss from free hypochlorous acid and hypochlorite ion alone. Experiments getting spectral UV absorption data for the UV shielding effect would also be helpful.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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