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Thread: erratic free chlorine loss?

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    erratic free chlorine loss?

    I recently completed a stenner pump project and am trying to fine tune it. Every day for the past couple weeks I've been checking my chlorine level with a FAS -DPD test ( using the 25ml sample and multiply drops by .2 to be as accurate as I can) Doesn't seem to be much rhyme or reason to it, but my daily fc losses are all over the board some times as little as 1.8 ppm per day but as much as 4.4 ppm per day. My question is: Is the variation in my results normal? Should I just aim to add 3 ppm per day? btw CYA has been constant @ 36-38 during entire testing period.
    15k gal inground Viking fiberglass pool; Hayward Variable 1.5hp pump (Maxflo VS); Hayward swimclear 325 sg ft cartridge filter; Raypak 206A 199k btu nat gas heater; Aquabot Bravo robotic pool cleaner

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    JasonLion's Avatar
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    Re: erratic free chlorine loss?

    A fair bit of variation is normal. Chlorine usage varies with the starting FC level, the amount of sunlight, and how many people are swimming. Sunlight can actually vary quite a bit without most people noticing. The idea is to tune your chlorine addition so the level the next day is still at least the minimum FC level for your CYA level.

    By the by, measuring FC/CC by steps of 0.2 is not really useful and it uses up your reagents more quickly. Steps of 0.5 are more than precise enough. In a similar vein, pretending that you can read the CYA test as finely as 36-38 is just an illusion. The test should be read to the nearest mark on the view tube, or 40 in this case. In both cases there are huge amount of "noise" in the system. You should not make the mistake of treating that noise as something that should be tracked.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: erratic free chlorine loss?

    Quote Originally Posted by JasonLion View Post
    A fair bit of variation is normal. Chlorine usage varies with the starting FC level, the amount of sunlight, and how many people are swimming. Sunlight can actually vary quite a bit without most people noticing. The idea is to tune your chlorine addition so the level the next day is still at least the minimum FC level for your CYA level.

    By the by, measuring FC/CC by steps of 0.2 is not really useful and it uses up your reagents more quickly. Steps of 0.5 are more than precise enough. In a similar vein, pretending that you can read the CYA test as finely as 36-38 is just an illusion. The test should be read to the nearest mark on the view tube, or 40 in this case. In both cases there are huge amount of "noise" in the system. You should not make the mistake of treating that noise as something that should be tracked.
    Thanks for the help.. I don't intend on testing to the .2 increment daily. I just wanted to set the chlorination system up to be as accurate as I can from the start. I have the stenner pump currently set to deliver 2ppm daily (during the early evening) I test my fc level daily at usually between 430 to 530 pm. After I test I aim for FC of 5ppm. Usually need to add just a little in addition to what the pump delivers but not always. CYA I am testing weekly for now and it seems to remain stable. Is this safe to test at intervals of two weeks?
    15k gal inground Viking fiberglass pool; Hayward Variable 1.5hp pump (Maxflo VS); Hayward swimclear 325 sg ft cartridge filter; Raypak 206A 199k btu nat gas heater; Aquabot Bravo robotic pool cleaner

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    Mod Squad tim5055's Avatar
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    Re: erratic free chlorine loss?

    Quote Originally Posted by echo View Post
    Thanks for the help.. I don't intend on testing to the .2 increment daily. I just wanted to set the chlorination system up to be as accurate as I can from the start. I have the stenner pump currently set to deliver 2ppm daily (during the early evening) I test my fc level daily at usually between 430 to 530 pm. After I test I aim for FC of 5ppm. Usually need to add just a little in addition to what the pump delivers but not always. CYA I am testing weekly for now and it seems to remain stable. Is this safe to test at intervals of two weeks?
    many only test CYA monthly or even a couple of times during the pool season. If you are not using any forms of solid chlorine or are adding CYA itself the reading should remain stable.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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