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Thread: Replacing water (high CYA) - what steps?

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    Replacing water (high CYA) - what steps?

    Hi Everyone,

    I have gotten very good a balancing my pool with the BBB method and using a good Taylor test kit.
    Over the past 4-6 weeks I could not keep enough chlorine and identified high CYA (~200) as the culprit.
    So this weekend I will drain about 2/3rds (or 8000G) of my pool and replace with fresh water.

    Questions:
    1. While the pool is near empty should I scrub the areas (like step corners) where little buildups of dirt, calcium and/or algea have set in? If so, what cleaners and method?
    2. Anything else to do maintenance wise with the plaster, skimmers etc?
    3. After draining - simply refill and start getting Alkalinity then ph, then Chlorine back in check?
    Build Mar '11: 12400 Gal, Gunite/White Plaster, Chlorine Pool with Spa and 3 Waterfalls over natural (sealed) rock. All Pentair Equipment: chlorine feeder, pumps and cartridge filter.
    Gets nearly 100% sun, no leaves, LOTS of wind, and plenty of sand from ongoing development around us.

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    Re: Replacing water (high CYA) - what steps?

    You will likely have to do repeat drain/refills to bring your CYA down to the recommended range.

    After your CYA is where it should be, adjust your pH to 7.2 or close to that, and SLAM your pool if those dirty areas you want to scrub are in fact algae. Worry about the TA and CH after the SLAM.

    Check pool school for how to take the needed steps.
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

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    Re: Replacing water (high CYA) - what steps?

    Sounds like you may need to SLAM after refilling if the FC was too low and you have seen algae.

    The order of adjustment after filling depends on the levels. Post results after filling.

    No real need to do any scrubbing while the pool is empty. I suppose you could if there was some stain or something.
    Jason, TFP Moderator
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    Re: Replacing water (high CYA) - what steps?

    No algea issues...just stains removed...
    Enclosed how my chems progressed during the about 80% refill over the weekend. I think it looks okay...
    Attached Images Attached Images
    Build Mar '11: 12400 Gal, Gunite/White Plaster, Chlorine Pool with Spa and 3 Waterfalls over natural (sealed) rock. All Pentair Equipment: chlorine feeder, pumps and cartridge filter.
    Gets nearly 100% sun, no leaves, LOTS of wind, and plenty of sand from ongoing development around us.

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    Re: Replacing water (high CYA) - what steps?

    I recommend lowering the ph to around 6 and brushing the pool really well. If the CYA has been high for a few years, you may find it to still be over 100ppm even after a full drain and refill.

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    Mod Squad jblizzle's Avatar
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    Re: Replacing water (high CYA) - what steps?

    Quote Originally Posted by Texasjeff
    I recommend lowering the ph to around 6 and brushing the pool really well. If the CYA has been high for a few years, you may find it to still be over 100ppm even after a full drain and refill.
    1. We would never recommend dropping the pH that low as it will damage the pool and equipment.
    2. If they did a full drain and refill, the CYA would have to be 0ppm.
    Jason, TFP Moderator
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    Re: Replacing water (high CYA) - what steps?

    jblizzle- you didn't just that say that did you? CYA builds up in the surface of the pool. By lowering the ph and brushing the pool as you're draining helps "release" more of the CYA. Not sure what your level of involvement is in the industry, but to think a temporary reduction of the ph to help remove CYA is instantly going to harm the pool and equipment is ridiculous. I operate an RO machine and have seen pools that the CYA was over 800ppm. I have also consulted with people that didn't want the RO because of price, but drained and refilled themselves without following any advice. They soon called me for more help.
    I have refrained from posting here in the past due to the lack of real experience most of you all possess. It's great you all can take care your pool. It's the only one that really matters. But to offer advice to so many others without proper experience and knowledge of their surroundings is not right.

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    Re: Replacing water (high CYA) - what steps?

    Quote Originally Posted by Texasjeff
    jblizzle- you didn't just that say that did you? CYA builds up in the surface of the pool. By lowering the ph and brushing the pool as you're draining helps "release" more of the CYA. Not sure what your level of involvement is in the industry, but to think a temporary reduction of the ph to help remove CYA is instantly going to harm the pool and equipment is ridiculous. I operate an RO machine and have seen pools that the CYA was over 800ppm. I have also consulted with people that didn't want the RO because of price, but drained and refilled themselves without following any advice. They soon called me for more help.
    I have refrained from posting here in the past due to the lack of real experience most of you all possess. It's great you all can take care your pool. It's the only one that really matters. But to offer advice to so many others without proper experience and knowledge of their surroundings is not right.
    How much CYA do you think will "build up" in the finish of a pool, and how much plaster needs to be eroded to remove it? Even if some CYA builds up on a pool surface it can't be a significant amount. Certainly not enough to be a problem upon re-fill with fresh water. What evidence do you have to support this? I would bet a hefty sum it wouldn't be enough to even register. We have lots of re-fill evidence here to strongly support the exact opposite of this build up theory you put forth.

    Taking your pH to 6 is not a good idea as a general suggestion for users of this board because it is hard on plaster to do so. Suggesting something like this to someone, especially an inexperienced someone is irresponsible at best.
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    Re: Replacing water (high CYA) - what steps?

    We have had many people do partial or full drain/refill to reduce CYA and never seen a significant CYA "sticking" problem. We've also had others who do Reverse Osmosis (e.g. Pool Services Technologies) and they never reported any need to brush or lower the pH to lower the CYA level in pools. That doesn't mean that some small amount of CYA does not adhere to some surfaces, but the amount must be too small to show up with any significance. If lowering the pH and brushing are part of the process of removal, then that implies that the "bond" is one of the negatively charged cyanurate ion since lowering the pH has it convert mostly to uncharged cyanuric acid. The following shows the concentration of the relative species at pH 7.5 vs. 6.0 (in the following, "CY" is the core de-protonated cyanuric acid ring so H3CY is cyanuric acid while H2CY- is singly negatively charged cyanurate ion):

    CYA Species .. pH 7.5 ....... pH 6.0
    H3CY ............. 17.71% ....... 87.03%
    H2CY- ............ 82.27% ...... 12.97%
    HCY2- ............ 0.014% ....... negligible
    CY3- .............. negligible ... negligible

    For simplicity, let's assume a 16'x32'x4.5' rectangular pool. The surface area of pool plaster is 944 square feet (87.70 square meters). The volume is 65242 liters so if 100 ppm (mg/L) of CYA were left on pool plaster surfaces that would be 6.52 kilograms (14.4 pounds) of cyanuric acid. The density of solid cyanuric acid is 2.50 g/cm3 so the volume of solid cyanuric acid would be 2616 cm3 so the thickness on the pool plaster surfaces would need to be 0.03 cm or 0.3 mm. Of course, the cyanuric acid wouldn't be binding to itself as it is soluble in water (saturation is several thousand ppm) but presumably bonded in some way as cyanurate to the pool plaster, but this amount seems unrealistically high.

    This paper describes various cyanurate derivatives and there are calcium and magnesium cyanurate salts, but they are moderately soluble in water as we know otherwise one could not have CYA in a pool with hard water without producing a precipitate. Pool plaster is largely a mixture of calcium silicate hydrate (C-S-H) and calcium carbonate. I can find nothing in the scientific literature with regard to cyanurate bonding to calcium silicate hydrate or pool plaster in general. That does not mean it does not occur, but that it has not been studied.

    We are generally very skeptical of these sorts of assertions ("CYA builds up in the surface of the pool") because there are so many myths in the pool/spa industry that turn out to be wrong. Not many people get their pools up to 800 ppm CYA so if this effect is a small one it might not show up significantly until the CYA levels get quite high as in the example given by TexasJeff. Also, if a neglectful pool owner never brushed their pool on a regular basis, especially if they had calcium scaling, then it is possible for such calcium scale to incorporate other compounds incidentally though the volume of CYA we are talking about here does again seem to make that implausible. Finally, if the CYA were over 800 ppm CYA, then ending up with 100 ppm CYA could easily happen if the pool was not drained completely since 100/800 = 12.5% so assuming (for simplicity) a 50/50 split 6 foot vs. 3 foot deep pool, this implies having no water in the shallow end and leaving a little over 1 foot of water in the deep end of the pool or the equivalent of that including the water found in pipes and filter (which is probably negligible compared to pool water volume). Is it possible that the people who claimed to have drained their pools did not fully drain them?

    Others have claimed that CYA settles to the bottom of pools yet we have not measured significant CYA concentration differences in pool water after any added CYA was thoroughly mixed. Note that without circulation, fresh rains can certainly cause a bifurcation of concentrations by diluting surface water leaving water at depth to be more concentrated and only mixing by diffusion which is very slow.

    Note that PPOA refers to "puddling and absorption in filter media, pipes, plaster and elsewhere retains small amounts", but the small amount was a result of 2 ppm CYA after draining from 50-60 ppm.

    I am not saying that the experience that is seen is not real -- just that the explanation for it may not be CYA bonding to plaster. We can certainly keep a close eye on this from the hundreds of pools that have partial or full drain/refill to see if any of them result in higher-than-expected CYA levels on a consistent basis.
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    Re: Replacing water (high CYA) - what steps?

    So I heard back from the owner of PST, another RO service, who confirmed that "Of the 100ís of pools that we have processed (all with some effect on CYA, no matter how high) we have never once seen it come back into pool readings after our process. Pools that came into range stayed there, and those that needed CYA added were brought up and held steady afterwards". They do not lower the pH nor brush the pool during the process.

    I suppose one could claim that the CYA is getting pulled out of the plaster on a continual basis during the RO process (fast enough for the timeframe that RO is done but not so fast that a drain of the pool would release it) in which case only experiments with high CYA pools that are quickly drained completely and refilled would be be definitive. Since we've got plenty of experience from pool owners in the 100-300 ppm CYA range who successfully lower their CYA levels as predicted without needing to lower the pH and brush their pools, it's sort of a moot point as to whether such techniques are needed when the CYA is 500-800 ppm or more since those situations appear to be pretty rare. Nevertheless, it would be good to get to the bottom of this so that we can either squash this myth for good or learn something new.
    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: Replacing water (high CYA) - what steps?

    I have performed several laboratory experiments about six years ago in regards to CYA loss (solubility issues in cold water) and/or bonding to pool plaster. Based on the results under controlled conditions, I suggest that there is not a measureable loss of CYA or a bonding with new or old plaster. My tests went to 300 ppm of CYA.

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    Re: Replacing water (high CYA) - what steps?

    chem geek and OnBalance,

    Thank you for your fine responses in this thread. It is important to all members that inaccurate and/or incorrect information get corrected quickly and openly.

    Your polite verbage and solid science that you both always present helps us all understand our pools better and confirms the validity of the TFPC methodology
    Dave S.
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    Re: Replacing water (high CYA) - what steps?

    Texasjeff, have you ever had a case where you completely drained and refilled a pool and then, when the pool was refilled, measured any significant level of cyanuric acid in the water?

    If yes, could you give the details, such as CYA before the complete drain and refill, and CYA level after?

    If you have multiple examples, I would be interested in hearing about those as well.

    Thanks.

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