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Thread: High use indoor pool chloramine problems.

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    High use indoor pool chloramine problems.

    Hi,
    You guys sure know your stuff re: pools, but I only see talk about backyard pools? Can I rack your brains and gain some insight on our pools?

    We have multiple 80K-120K gallon, high use (15+ hours/day)/high temperature (+85*F) indoor pools.

    I've spent hours trolling this site and the others that are mentioned in the various threads and I really appreciate the level of sophistication you all display.

    Our biggest issue is with our indoor pools and the chloramines. We keep a high FC residual (3-5ppm) to combat the many young and old bodies in our water. We would like to be able to run lower levels of chlorine and not have use 20+ gallons of Sodium Hypo to shock the pool.

    The powers that be are ready to dump tons of money on a UV system to combat the CC's because it is rare to see CC levels <1.0ppm using the 10x shock method. We know our air systems arent adequate and improving that is also on the table.

    I have read that some suggest to keep a small residual of CYA in an indoor pool, but my techs gasp at that notion. I have heard that a weekly use of KMPS (non-chlorine shock) is an option but the techs tell me that it is too expensive and it will throw off the ORP sensors.

    Most of our pools use either Sodium Hypo or Calcium Hypo and Muriatic acid or CO2. Currently they are diluting the water and shocking at 10X CC levels (with windows/doors open and fans blowing over the water) to control the chloramines.

    I should mention that we arent afforded any down time except overnight and the longest window to do the shocking is only 15 hours. This creates a problem when we have to add high amounts of chlorine that need to be neutralized before the pool is opened the next day.

    Thank you,
    Josh
    16X32 in-ground 15,000 gal. vinyl grecian, 24in jacuzzi filter w/1.5hp jacuzzi pump and Aquarite swg.

  2. Back To Top    #2
    JasonLion's Avatar
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    Welcome to TFP!

    Around here we focus on residential pools, which are almost all outdoor pools. I can give you an overview of indoor pool issues, but the bulk of my knowledge is focused on outdoor pools.

    Using CYA in an indoor pool is heresy but it can have some significant advantages. Perhaps Chem Geek will stop by and provide enough information to convince your techs. Low CYA levels will slow the production of CC and reduce chlorine side effects on bathers (bathing suits last longer, fewer people have allergic reactions, less hair damage).

    My first choice would be MPS, but the use of ORP sensors rules out MPS. MPS isn't as expensive as it might seem because you will be able to shock less often and so save some money that will partially or full compensate.

    Have you thought about getting a SWG system? That would be a major change/expense, but would help significantly with CC levels. Indoor use of a SWG system requires some care, so that FC levels don't get too high, but otherwise simplifies things.

    That leaves UV and ozone systems. Both can help significantly with CC and both will also tend to break down some of the FC, requiring the use of additional chlorine to maintain levels.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Josh, welcome to TFP!!

    The guy you want to hear from is chem_geek - while he's not a pool chemist by trade, he knows!! this stuff. He's the one who has recommended ~ 20 ppm cya in indoor pools, and though I can't reproduce the reasoning (his posts), I have found it to be sound and reasonable and workable! Some of what is recommended here 'flies in the face' of traditional NSPI (or whoever) methods, but the fact is that they work! Waterbear may also chime in with his thoughts (he also really knows the chemistry side of pools) and there are some others who either have or have knowledge of indoor pools and how to deal with them. It is my understanding that you can reduce the chloramines with a non-chlorine shock, but they have certain 'provisos' that I'm not qualified to explain

    If none of the 'experts' responds by tomorrow, I'll give them a PM to get their attention and get you the expert help you've come here for
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

  4. Back To Top    #4
    I have absolutely nothing to add, except to say welcome to TFP!

    8000 gallon 20' x 48" round vinyl frame pool, 12" sand filter (don't have the specs on the pump), TF100 test kit
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    "Shock" is a process, not a product!

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    Josh,

    First of all, welcome to TFP!

    As for persistent chloramines, I can't say that the theory I'm about to describe has been proven with indoor pools. The only thing that has been shown, in spas, is that using too much CYA leads to regular Combined Chlorine readings since the breakpoint reaction is slowed down too much. At the other extreme with too little CYA, the problem is that this produces more of the nastier and smellier dichloramine and nitrogen trichloride (trichloramine) products in addition to monochloramine, but this part has not been proven.

    Basically, in a nutshell, CYA acts as a chlorine (hypochlorous acid, specifically) buffer and moderates its concentration significantly. You can see in this post the traditional industry graph of HOCl/OCl- which only really applies in a pool with no CYA and then I show the true graph in the presence of CYA. In a pool with 3.5 ppm FC and 30 ppm CYA and a pH of 7.5, for example, 97% of the chlorine is bound to CYA in a series of chemicals called chlorinated cyanurates that are not effective sanitizers nor oxidizers. 1.5% is hypochlorite ion, OCl- while only 1.5% of the FC is hypochlorous acid which is disinfecting chlorine. Free Chlorine (FC) measures not only hypochlorous acid and hypochlorite ion, but also all of the chlorinated cyanurate species as well.

    I write more about this including some analogies to hopefully make it easier to understand in this post on another forum (just focus on the section "Chlorine and Cyanuric Acid (CYA)" unless you are interested in the rest).

    The bottom line is that with 3-5 ppm FC in a pool with no CYA, you are over-chlorinating the water. This makes the breakpoint reaction happen too quickly so results in a higher production of disinfection by-products, according to breakpoint chlorination models I have (I use two different ones and am still looking for even better ones). As an example, let's say you have 4 ppm FC at 87F temperature and a pH of 7.5 and 0.1 ppm ammonia (as Nitrogen -- equivalent to 0.5 ppm combined chlorine if turned into monochloramine). The following table shows what happens with no CYA and with 10 ppm CYA. The numbers are in pairs since there are two breakpoint chlorination models I have and they produce different results -- I think the second in the pair might be more accurate. [EDIT] I've added a third number that is probably the most accurate since it is from the most recent and comprehensive model of breakpoint chlorination. [END-EDIT]

    .................................... 0 ppm CYA ................................................. 10 ppm CYA
    Chemical ........... Peak Time ....... Concentration ................... Peak Time ....... Concentration
    Chlorine ................ 0 sec ............... 4 ppm FC ............................ 0 sec .................. 4 ppm FC
    Ammonia .............. 0 sec ............... 0.1 ppm NH3-N ................... 0 sec .................. 0.1 ppm NH3-N
    Monochloramine .... 3 sec .............. 360 ppb ........................ 10 / 10 / 27 sec ............ 360 ppb
    Dichloramine .... 30 /140 / 48 sec ... 80 / 265 / 73 ppb ............ 1 / 6 / 7 min ............. 15 / 83 / 59 ppb
    Nitrogen trichloride . 10 / 15 / 4 min .. 1.6 / 9.3 / 122 ppb ..... 20 / 40 / 8 min .......... 0.15 / 1.1 / 13 ppb
    50% Breakpoint .... 140 seconds (2.3 minutes) ........................ 21 minutes
    90% Breakpoint .... 400 seconds (6.7 minutes) ........................ 64 minutes

    Note that after breakpoint is complete, the ammonia, monochloramine and dichloramine will go to zero, but the nitrogen trichloride will remain persistent (though it is quite volatile and very smelly and irritating). Though the above would explain why indoor pools with no CYA (as well as a lack of sunlight and poor air circulation) would have more problems with smelly chlorine and people having respiratory problems, eye irritation, and asthma, it doesn't really explain large quantities of combined chlorine.

    I think that may be coming more from other compounds other than just simple ammonia. For example, urea, which is ammonia-like but may not behave as described in the above model, as well as other organics. Usually, chlorine doesn't combine that quickly with other organics unless the chlorine concentration is high, which is the case in pools without CYA.

    So in order to reduce the rate of all chemical reactions with chlorine and to make the pool sanitation more consistent with that of outdoor pools, I propose using a small amount of CYA to moderate the disinfecting chlorine level. Even 10 ppm CYA will cut down the disinfecting chlorine level significantly. 4 ppm FC with 10 ppm CYA has the same disinfecting chlorine level as 0.5 ppm with no CYA. So all reactions, including the formation of perhaps more persistent combined chlorine, will be around 8 times slower and the final quantities will be about 1/8th in amount. It will still be relatively fast, but will reduce the creation of disinfection byproducts.

    So while using the CYA makes a lot of sense to reduce corrosion, oxidation of swimsuits and hair, and production of disinfection of byproducts (all of which depend on the effective disinfecting chlorine or hypochlorous acid concentration), I don't know if it will significantly reduce the production of Combined Chlorine that you are seeing. My guess is that it will, but we don't have any test case that has proven that (as I said before, we've seen the opposite case of too much CYA causing Combined Chlorine, specifically monochloramine, and then lowering the CYA to a more reasonable level of 4 ppm FC with 20 ppm CYA made the CC go away, but the case of no CYA vs. a small amount of CYA we haven't proven in real pools yet).

    Just as using MPS will artificially inflate the ORP which is not good for your automation of chlorine dosing, the use of CYA will also affect the ORP by lowering it, BUT it will be a legitimate measurement of what is going on because right now you are overdosing in chlorine. ORP sensors are unfortunately inconsistent, but 4 ppm FC with no CYA is 1.9 ppm hypochlorous acid and will report 812 mV ORP on Chemtrol, 803 mV ORP on Oaktron, 869 mV ORP on Sensorex. With 10 ppm CYA the same 4 ppm FC is 0.25 ppm hypochlorous acid and will report 746 mV ORP on Chemtrol, 719 mV ORP on Oakton, 622 mV ORP on Sensorex. It is still plenty for sanitation as most outdoor pools operate closer to 3.5 ppm FC at 30 ppm CYA which is 0.05 ppm hypochlorous acid and will report 695 mV ORP on Chemtrol, 654 mV ORP on Oakton, 428 mV ORP on Sensorex. The Sensorex data was taken from a table they posted on the web so I suspect it's just plain wrong. The Oakton data is from actual field data from a portable Oakton sensor. The Chemtrol is from data on the web, but where they appeared to do a decent job measuring their sensor in a variety of conditions. So you'll have to "recalibrate" your ORP controllers to achieve your target 3-5 ppm FC level after you've added the 10 ppm CYA since the target ORP will be lower.

    By the way, the 10x rule for breakpoint of chlorine is wrong -- another one of those industry myths where it starts out with some correct information and then gets twisted somewhere along the way. The correct rule comes from the fact that it takes 1.5 times the amount of chlorine, on a molecule per molecule basis, to achieve breakpoint with ammonia as indicated below:

    2HOCl + 2NH3 --> 2NH2Cl + 2H2O
    HOCl + NH2Cl --> NHCl2 + H2O
    NHCl2 + NH2Cl --> N2(g) + 3H+ + 3Cl-
    -----------------------------------------------------------------------------------------------------------------------
    3HOCl + 2NH3 --> N2(g) + 3H2O + 3H+ + 3Cl-
    Hypochlorous Acid + Ammonia --> Nitrogen Gas + Water + Hydrochloric Acid (as ions)

    Ammonia is typically measured in units of ppm Nitrogen which is 14.0067 g/mole while chlorine is measured in units of ppm Chlorine Gas, Cl2(g), which is 70.906 g/mole. So it takes 1.5*70.906/14.0067 = 7.6 times more ppm of chlorine to oxidize (achieve breakpoint with) a ppm amount of ammonia. Original experiments found that using 8-10 times worked best so that's where the original 10x rule came from.

    BUT, note that the above rule uses a measurement of ammonia based on ppm Nitrogen. The rule for pools uses Combined Chlorine which is a measurement in units of ppm chlorine (gas), NOT ppm ammonia-nitrogen. One monochloramine or other combined chlorine molecule will measure the same as one molecule of chlorine in water. So because they are the same units, the real factor would appear to be just 1.5, but even this isn't quite correct because Combined Chlorine isn't measuring ammonia but monochloramine (or it's equivalent). As you can see from the reactions above, one molecule of chlorine combines with ammonia to produce monochloramine so when measuring Combined Chlorine you've already used up 1.0 of the 1.5 you need. So technically, you only need 0.5 times the Combined Chlorine amount to achieve the rest of breakpoint and even rounding up and being conservative this would be just 1 for 1 -- a Free Chlorine (FC) that is equal to Combined Chlorine (CC).

    In fact, in most pools and spas, there is continual breakpoint and it doesn't require anything near 10x the Combined Chlorine even when it measures a relatively small amount. I think that the 10x rule has persisted at least partly because in pools with CYA the breakpoint reactions are slower, as I had indicated earlier, so by using a higher level of chlorine one speeds up the reactions. At least with CYA in the water, one doesn't go overboard and produce a lot of disinfection byproducts. The bottom line is that hopefully with a little CYA in the water, you won't be seeing Combined Chlorine build up, but you could see it temporarily after bather loads and then drop down in the hours after such load has dropped off. At least that's the hope. And yes, air circulation is very important to helping the breakpoint reaction proceed well. When airing out the pool to reduce CCs, especially if you smell anything chlorine-like, then you should run the pump and point the returns up and otherwise aerate the water to remove the volatile compounds. Note that the pH may rise if you do this (depending on your TA level).

    If you have a smaller pool you can use as a "test", then that obviously would be the best way to go. Be sure to let us know what happens and report your progress. It may take some time to get the Combined Chlorine down initially, but the key will be to see if it keeps getting created at the same rate when CYA is present -- that is, if it doesn't rise as much as you've been seeing.

    There is no question that UV from sunlight keeps Combined Chlorine in check so that using a UV system should help in that regard considerably, but I hope you try the CYA to see what happens. Even if it doesn't help with the CC, then as long as it doesn't hurt it's actually much better and healthier for your swimmers and not as harsh on your equipment (for corrosion).

    By the way, you can use Dichlor as a fast way to add both chlorine and CYA since it dissolves readily, but it is a more expensive source of chlorine and CYA (see this link for a CYA cost comparison and this link for a chlorine cost comparison). For every 10 ppm FC added by Dichlor it also adds 9 ppm to CYA. Pure CYA is the least expensive, but dissolves very slowly so the fastest way is to hang it in a panty hose or sock over a return flow so it will take a day or two instead of a week to dissolve. I only recommended 10 ppm CYA in what I wrote in this post so that your techs wouldn't freak out and would be able to more readily dilute a pool back towards zero CYA if you changed your mind, but really 20 ppm CYA is a more reasonable number if things work out for you. This is not only measurable with some CYA (manual) turbidity tests, but it further reduces disinfecting chlorine by a factor of 2 while still being plenty for disinfection (and algae prevention).

    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"

  6. Back To Top    #6
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    there isn't much that I can add. Richard really covered just about everything. The UV is certainly a good addition for combating the CC, IMHO probably more effective than ozone, which I would not suggest with the inadequate air handlers you said you now have.
    The only other thing I have to say is Welcome to TFP!

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    Quote Originally Posted by chem geek
    (I use two different ones and am still looking for even better ones)
    Can this be of help?

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    Hi to everyone!

    Wow, I knew I was in for it. I'll get to reading and post back shortly.

    Thanks to all who replied.
    16X32 in-ground 15,000 gal. vinyl grecian, 24in jacuzzi filter w/1.5hp jacuzzi pump and Aquarite swg.

  9. Back To Top    #9

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    Quote Originally Posted by CaOCl2
    Quote Originally Posted by chem geek
    (I use two different ones and am still looking for even better ones)
    Can this be of help?
    I've seen that one before, but some of the numbers don't make any sense at all so I think there are transcription errors in it. It is a model that I'm looking for with more complete explanation. Just for the heck of it, I'll put it into my spreadsheet to see what happens. I need to convert the "per hour" to "per second" as that is more standard, but we'll see what happens. Thanks for the link.

    Unfortunately, they do not give a value of kH in the equation for kd. Also, the constant k6 has an M-2 term yet there are only two reactants and constant k7 has an M-1] term yet there is only one reactant so either the units are off or the rate formula contains additional terms that are not derived from the equation as listed. So I can't really use this model as is. I think that's why I didn't use it the last time I saw this webpage. The model also does not show the formation of NCl3 though that may be one of the "products" which unfortunately are not explicitly listed (obviously some are N2 and H+ and Cl-).

    The rate constants for the models I am currently using (Wei & Morris and Selleck & Saunier mostly though I also have Stenstrom & Tran that I usually don't use) have temperature dependence so are more useful in that regard, but if this Jafvert/Valentine/Vikesland model were better documented and more consistent, I'd use it. At a temperature of 77F (25C), I get the following rate constants for the different models where they all refer to the same equation (the last one is the model given in your link -- converted to "per second" from "per hour"):

    ( 1 ) 6.13x106, 6.13x106, 6.13x106, 4.17x106
    ( 3 ) 4.23x102, 3.46x102, 4.23x102, 2.78x102
    ( 7 ) 3.52x10-2, 1.21x10-3, 1.21x10-3, 1.11x102
    ( 8 ) 2.40x104, 5.19x104, 2.40x104, 2.78x104
    ( 9 ) 2.21x103, 4.00x103, 2.00x103, 8.33x103

    The number I've put in bold above from the model in the link you gave is suspect and is also a very critical parameter since it is the rate-limiting reaction that is what makes breakpoint take as long as it does and also determines, indirectly, the amount of disinfection by-products. So it is obviously important to sort that out.

    [EDIT] I wrote to Dr. Valentine and he referred me to his paper from which the link you gave was a subset. It cost $25 to get the paper (too bad scientific literature isn't free -- well, it is if you go to a library that has a copy) and I've got the full data now. The difference in rate constants for equation 7 is explicitly mentioned in the paper (as a factor of 1000 -- the end result isn't that different due to different "escape" reactions that don't involve the intermediate). So I'm updating my spreadsheet to incorporate the new model. [END-EDIT]

    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"

  10. Back To Top    #10

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    Quote Originally Posted by Jadams9622
    Hi to everyone!

    Wow, I knew I was in for it. I'll get to reading and post back shortly.

    Thanks to all who replied.
    Your welcome. One more thing I thought of that we discovered in this thread that had an indoor pool with an SWG with persistent combined chlorine (among other things such as corrosion issues) was that this Combined Chlorine did not go away (using bucket tests) with airing out (so the CC wasn't volatile), with shocking with chlorine (including the SWG with its superchlorination), with exposure to UV from lamps from a tanning bed (though the FC dropped, as would be expected), with adding MPS (though interestingly the MPS got reported as FC, not CC). The only thing really unusual about the pool was an extremely high level of phosphates so *maybe* they are interfering with the CC test, but that's just speculation on my part. You might, for the heck of it, test your pool's phosphate level.

    When CCs are so persistent that seemingly nothing makes them go away, then they are probably not a problem and are either some sort of test error from interference or are relatively inert CCs (at least one would hope; you're not drinking the water anyway). Of course, that doesn't mean much to a public health inspector so in the worst case dilution would be the only way to reduce the CC.

    You might try taking a bucket of pool water and doing various tests on it to try and get rid of the CCs. I suspect that shocking with chlorine won't do anything. Exposure to the UV from sunlight would be interesting. If that gets rid of it, then a UV lamp system might help, but if even sunlight doesn't get rid of it then probably nothing will (other than dilution).

    The hope with using CYA in the indoor pool is that such persistent CCs don't form in the first place or at least not as quickly.

    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"

  11. Back To Top    #11
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    Quote Originally Posted by chem geek

    The only thing really unusual about the pool was an extremely high level of phosphates so *maybe* they are interfering with the CC test, but that's just speculation on my part. You might, for the heck of it, test your pool's phosphate level.
    I would possibly suspect high nitrate levels in this particular case (although testing did indicate there were none.) Nitrates are not usually tested in pool water and high nitrate levels are often found along with high phosphate levels (But not always!). High nitrate levels can cause persistant CC and a high chlorine demand.

    Hach and LaMotte are the only two companies that offer a nitrate test kit specifially for pool/spa water but the Taylor K-1128, although somewhat complicated, is certainly useful and extremely accurate. Hach has the AquaChek nitrate test strips, which certainly can tell you if nitrates are present (but I would not count on them for a quantitative measurement) and LaMotte offers the 3465 kit which has a 0-80 ppm nitrate test and a 0-1000 ppm phosphate test.

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    Evan (from farrrr left field) - would 'peeing' in the pool, by those too young to understand that pee shouldn't be added to pool water, constitute the nitrates/ amonia which might cause what you were talking about?
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

  13. Back To Top    #13
    FYI

    Phosahate test kit:
    Taylor K-1106....about $20
    found online

    Nitrate and Nitrite test kits:
    Nutrafin NO3 and NO2....about $15 each
    found at local pet store, you can also get the phosphate kit at the pet store
    21,000 gal Fiberglass (Indoor)

  14. Back To Top    #14
    Hi again,
    That is some really interesting information posted and linked. I'm currently taking Chemistry and some of this actually makes sense. Although I admit I dont totally understand it all.

    I ran this information by our techs and got negative feedback re: using CYA in indoor pools as expected. Their reasoning was that the CYA doesnt go away in an indoor setting without dilution, would throw off the ORP readings and would also force us to use more chlorine.

    None would agree to use their pools as a test but they did agree that we try the bucket test with CYA and also test our pools for nitrates and phosphates. I'm not sure doing a bucket test with CYA will work but I am interested to see what the nitrate and phosphate levels are and if removed what the effect on CC's will be.

    I have looked into the KMPS (non-chlorine shock) and it looks promising. We will need to use a special test kit to remove it from the sample when testing for FC and CC but I am not sure if the effect on our ORP readings is worth it.

    We have some pools slated for UV systems this year and if that ends up being the total solution that the salesmen are claiming then we will most likely go that way.

    I appreciate the help but it looks like they will have to start teaching that CYA in indoor pools isnt taboo in the CPO and AFO classes before our pool techs will listen.

    Thanks,
    Josh
    16X32 in-ground 15,000 gal. vinyl grecian, 24in jacuzzi filter w/1.5hp jacuzzi pump and Aquarite swg.

  15. Back To Top    #15
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    Quote Originally Posted by Jadams9622
    I ran this information by our techs and got negative feedback re: using CYA in indoor pools as expected. Their reasoning was that the CYA doesnt go away in an indoor setting without dilution, would throw off the ORP readings and would also force us to use more chlorine.
    It probably doesn't matter at this point, but those aren't really valid points (except in one way).

    It is true that the CYA doesn't go away except by dilution. That isn't a problem in and of it's self. It would cause problems if you tried out CYA and then decided not to use it, since you would then need to drain and refill the pool. This is the one possible disadvantage, and that only if the CYA doesn't work out. Other than that it is actually convenient (add CYA once and then don't worry about it much).

    Adding CYA does change the ORP reading, but not in a way that causes any problems. Once you add CYA the ORP reading will go down and you need to raise the FC level to bring the ORP reading back up. Any ORP based automation system will take care of this automatically, doing the correct thing by default. No change in operations is required. This is very different from MPS, which changes the ORP reading in a way that can not easily be compensated for.

    And finally, there will not be any significant long term change in the amount of chlorine required. You will need to add extra chlorine once to bring the FC level up after adding the CYA. Once that happens the rate of chlorine consumption will remain essentially the same as it was before.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  16. Back To Top    #16

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    Quote Originally Posted by JasonLion
    Adding CYA does change the ORP reading, but not in a way that causes any problems. Once you add CYA the ORP reading will go down and you need to raise the FC level to bring the ORP reading back up. Any ORP based automation system will take care of this automatically, doing the correct thing by default. No change in operations is required. This is very different from MPS, which changes the ORP reading in a way that can not easily be compensated for.
    Assuming that the ORP is set to some reasonable level and that it is indeed set correctly, then this is true. But then, 650 mV (with a portable Oakton sensor) would be 0.1 ppm FC with no CYA and I doubt that this is the level that was being maintained in the pool. If it was, then this is a reasonably low chlorine level BUT it's hard to maintain consistently and can get used up locally rather quickly from bather load. So normally one sees something closer to 1 ppm FC in indoor pools with no CYA, but that is over-chlorinating (and is closer to 750 mV). Josh, your pool has 3-5 ppm FC with no CYA which is more like 790 - 812 mV ORP which is extremely high. My proposal of using 4 ppm FC with just 10 ppm CYA is roughly 720 mV and plenty for disinfection.

    So given your current "standard" at 3-5 ppm FC with no CYA, I suspect that your techs are ignoring any calibrated very high ORP reading and instead just "set" the ORP point to correspond to whatever produces the 3-5 ppm FC (maybe their ORP sensor lets you define an FC setpoint instead and you just calibrate to an FC directly -- it then uses ORP internally to get back to that same "set" ORP value). So adding 10 ppm CYA will lower the ORP that produces 4 ppm FC, but they can very easily adjust that setpoint.

    The bucket tests can only help you determine what might get rid of your Combined Chlorine, but you can't use a bucket test to simulate the prevention of that Combined Chlorine in the first place since you need to have bather load to do that.

    I worry a bit about the people who are using those pools. They are getting exposed to high chlorine levels, even for most indoor pools. If you want to show your techs the difference, take two buckets, one with 4 ppm FC and no CYA (i.e. your current pool water) and another with that same water but adding 10 ppm CYA to it (this is hard to do -- it's only 1/120th of a teaspoon in one gallon; so first mixing one teaspoon in one gallon of fresh hot water and thoroughly mixing which takes a while to dissolve and then taking one fluid ounce of that and adding it to a bucket of pool water would be about 10 ppm CYA). Then add a paper clip (zinc coated, as most are) to both buckets. Notice the difference after 1 day, several days, a week, several weeks (you have to maintain the chlorine level in each bucket). That difference in corrosion is what is happening to your patron's skin, hair, swimsuits, etc. The ORP reading also tells the same story -- CYA does NOT directly interfere with the ORP sensor. The ORP is simply measuring something akin to the disinfecting chlorine (hypochlorous acid) level and it is way too high in a 4 ppm FC pool with no CYA.

    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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