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Thread: Question about FC

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    Join Date
    May 2013
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    New Jersey
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    Question about FC

    We strictly use liquid chlorine. We seem to lose about 2 ppm per day. I always test the chlorine around 4:30 pm every day and it's almost always down to 3 from our target of 5 (at least I think it's at 3..read on). Now, the problem is my eyes deceive me sometimes where I can't tell if it's at 3 or 4, using the TF-100 kit. I must look at it a million times before choosing which number it's closer to, normally just going with 3 as I feel it's better safe to have a little more chlorine than not enough. I surely don't want to use my FAS/DPD chlorine test for this as it's surely not worth wasting it! Here's my question...If you consistently go over your FC target level every day by a small amount, is there any harm in that? I certainly don't want to over-chlorinate, but I can't imagine that my levels would be that much higher than our target, if at all the way I have been doing it. Just thinking if sometimes my FC is actually at 3.5 or 4, but I am calculating it at 3, can that cause any issues anywhere along the line?

    Our CYA is 40, so our target it 5 and minimum is 3.
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: Question about FC

    The imporant thing is to make sure that you don't allow the fc to get too low. Being a little high is fine and good insurance.

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    Re: Question about FC

    Any tips on how to tell exactly what the number is on the test? I use a white background but that doesn't seem to help ... Just one of those things, I guess!
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    Re: Question about FC

    If you want precision and accuracy, use the FAS-DPD. Stock up on reagents, they're not that expensive.

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    Charlie_R's Avatar
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    May 2013
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    Mexico, MO
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    Re: Question about FC

    Have you tried using the DPD powder and FAS drops yet? It seems you are describing using the K-1000 unit of your TF-100.

    This is fine to do, however if you have questions about the OTO results, then use the FAS-DPD to confirm. Remember, you can use the 10 ml sample size to save on reagents.
    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: Question about FC

    I was avoiding using the FAS-DPD so I could save it for shock time I already used a bit of the powder last time we shocked and would like to preserve it if I can

    I am a testing maniac, so I will surely be stocking up on everything before the season is over!
    7+ years, inground, 25,000 gallon, vinyl, sand filter.

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    37,879

    Re: Question about FC

    Very few people can distinguish any level between 3 and 8 using the OTO chlorine test (from the K-1000).

    Another approach is to use the FAS-DPD test weekly to get exact numbers and figure out how much to add daily, and then use the OTO test daily just to check that you are on track without noting the exact level.
    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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