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Thread: SWG and HIGH FC reading

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    SWG and HIGH FC reading

    I've been reporting on my success with the Intex SWG over in this thread: http://www.troublefreepool.com/viewt...hp?f=21&t=1090

    To recap, I've had the SWG for a little over a week, been reading FC at 5+ (off the high end of the scale on DPD tester). Earlier this week, I finished adding borates to the pool, and just today received the FAS-DPD reagents and powder necessary to test higher and more accurate FC measurements. After testing my chlorine levels with the FAS-DPD method twice for accuracy, the levels seem a little bit high. These are my most recent numbers:

    FC 11.2
    TC 11.2
    PH 7.5
    TA 75
    CH 250
    CYA 50
    BORATES 50
    SALT 3550

    I'm kind of amazed that we haven't been experiencing more eye discomfort with this level of chlorine, and now that the borates are in the water, there is absolutely zero eye discomfort and the water has a new found clarity unlike anything I've ever seen in a pool. Just in case you're not familiar with the Intex SWG, it only has a digital timer that allows the number of running hours to be programmed between 1 and 12, but there is no way to adjust the percentage of electrolysis that takes place during the running hours. Once this is set, it will repeat the same cycle at the same time every day, but judging from the 11.2 FC reading I measured, it doesn't seem necessary for me to continue running the SWG for the manufacturer's recommended 12 hours for our 24' round pool.

    As far as coming down from this current set of measurements, is it best to not run the SWG at all until the level comes down and then experiment with the run times, or should I just start running the SWG for less hours each day? Is there any danger in letting the kids swim while the FC is this high?

    Thanks for all of the great help this forum has given me already!!
    24' X 54" Sharkline Oceanic AGP - installed 24" below ground level
    Waterway 2HP 2 Speed Pump (running at .25HP low speed 90% of the time)
    Sparco Hydromatic Media Filtration (120 sq ft cartridge) with Skim Filter
    Intex SWG (purchased June 2008, model #56601E)

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    JasonLion's Avatar
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    Re: SWG and HIGH FC reading

    FC doesn't cause any irritation except at far higher levels. CC is the primary cause of irritation. Your high FC levels are driving CC to zero.

    The SWG is getting so far ahead because of the borates. Borates reduce chlorine consumption.

    With the Intex SWG you adjust the number of hours in the same way you adjust the percentage on a typical SWG. If the FC level is too high reduce the number of hours. If the FC is too low increase the number of hours. Just turn down the number of hours and give it a couple of days to get into balance at a new lower level before testing and adjusting it again.
    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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    Re: SWG and HIGH FC reading

    Thanks for a quick response time, Jason. I thought that the percentage dial on other SWG's affected how much voltage was used in the electrolysis process and the Intex just ran wide open for as many hours as I set the timer. I appreciate you educating me about the Intex timer function vs. other SWG's dials and percentages. It prompted me to do even more reading.

    Based on what you're saying about the borates lightening the work load on the FC, I'll try setting the timer back to something like 8 and see if the FC starts to come down. What would be a good level of FC to try to maintain with a CYA level of 50?

    My only other concern with a high FC level is the accuracy of the pH testing, but I don't have any indicators that are telling me that anything is outside of normal.
    24' X 54" Sharkline Oceanic AGP - installed 24" below ground level
    Waterway 2HP 2 Speed Pump (running at .25HP low speed 90% of the time)
    Sparco Hydromatic Media Filtration (120 sq ft cartridge) with Skim Filter
    Intex SWG (purchased June 2008, model #56601E)

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    JasonLion's Avatar
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    Re: SWG and HIGH FC reading

    Most SWG run the given percentage of the time the pump is on. For example, they might turn on for the percentage number of minutes out of every 100 minutes, while the pump is running. There are a few that adjust either the voltage or the number of plates that are energized, but that is the exception.

    None of that really matters. What matters is that both the percentage setting and the number of hours setting control the amount of chlorine produced. Higher percentages and higher numbers of hours mean more chlorine.

    With a CYA of 50 and a SWG, you want FC to be at least 2 at all times. I would aim for 3 when measured in the early evening after a sunny day.

    You might want to raise the CYA level a little. CYA with a SWG should be between 60 and 80 for the best balance between cell life and high CYA level issues. Lower CYA levels mean shorter cell life.

    The Taylor chemistry, used in Taylor and TF Test Kits kits, is listed as measuring PH when FC is up to 15. There seem to be small biases in the PH reading starting when FC is around 10, but serious errors don't begin until FC is in the 20s. With FC at 11.2 your PH reading will be off by no more than +-0.15, probably less (assuming you are good at comparing colors), so it is reasonably precise in your situation.
    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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    Re: SWG and HIGH FC reading

    Thanks again for getting back to me so quickly. I only ran the SWG for 6 hours last night, and I'll get a fresh set of test measurements later this evening.

    When I read the Water Balance tips for a SWG posting by waterbear, I did see that the recommended CYA level mentioned is 60-80 for most manufacturers. I already bought another 3 lbs. since according to the pool calculator, another 3 lbs. of CYA should get my 14,400 gallons up to about a 75 CYA level. The manual that came with the Intex SWG says they recommend a CYA level between 30-50, so I was halfway afraid to go any higher than 50. Do you guys think it is better to treat this SWG just like any other, and apply the chemistry that works best for most? I suppose I'm a little bit late to be asking that question, since the Intex manual recommended a minimum TA of 100, and I lowered ours down to 70 for purposes of buffering the pH rise I was experiencing and also to get to a comfortable TA level prior to adding the borates, but I would still like to hear if the general feeling is to go with chemistry that works for the majority of SWG's and try to get longer life out of this Intex SWG.
    24' X 54" Sharkline Oceanic AGP - installed 24" below ground level
    Waterway 2HP 2 Speed Pump (running at .25HP low speed 90% of the time)
    Sparco Hydromatic Media Filtration (120 sq ft cartridge) with Skim Filter
    Intex SWG (purchased June 2008, model #56601E)

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    JasonLion's Avatar
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    May 2007
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    Re: SWG and HIGH FC reading

    Different SWGs can require different salt levels and systems that include an ORP sensor require lower CYA levels. Other than that, all of the levels behave in the same way regardless of which SWG you have.
    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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    Join Date
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    Re: SWG and HIGH FC reading

    Bob, welcome to TFP!!

    Jason has given you excellent! advise. With your using borates as the pH source, the lower TA will not be an issue
    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!)

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