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Thread: OCLT and FAS-DPD Accuracy Question

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    OCLT and FAS-DPD Accuracy Question

    I see that for an OCLT the overnight FC loss should be 1.0ppm or less. However, when doing a SLAM with FC in the ~20-25ppm range, how accurate is the FAS-DPD testing? I read that it is +/- 10% accurate. Accurate enough for the lower FC levels, but at 25ppm that can be +/- 2.5ppm. Therefore, the testing accuracy is less than what the OCLT test requires. Any thoughts?

    I've seen some info on this, but nothing definitive.

    Thanks
    St, Augustine, FL / Covered Screen Enclosure
    1982 IG plaster/pebble - 18K gallon city water, Hayward C900 Cartridge Filter, Single Speed Pump 1.5hp
    Testing with TFT-100, Treated with Liquid Chlorine, Muriatic Acid, and Baking Soda

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    TFP Guide

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    Re: OCLT and FAS-DPD Accuracy Question

    Never had to think about it, so if someone with SLAM experience chimes in I would taker their advice over my guess, but absent a better idea I think I would mix 100 ml of pool water to 100 ml of non chlorinated drinking water and use that mixture for my 10 ml sample. Test results should be 1/2 of true levels but still give you the accuracy you are looking for.
    12,300 Gallon, IG PebbleFina, 3 ft sheer, 2 Jandy nicheless LED lights, Jandy Pro 1.5HP VS pump (A.O. Smith Motor), PB4-60 Booster pump, Polaris 280, Jandy cv340 cartridge filter, Zodiac Z4 control panel W/iAquaLink, Stenner pumps for chlorine & MA connected to WiOn WiFi switches, TF-100. You can support TFP with AmazonSmile just click the link!

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    Mod Squad woodyp's Avatar
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    Re: OCLT and FAS-DPD Accuracy Question

    Are you sure you're not referrring to +/- accuracy on the CYA test instead?
    16x32x52" Steel Cornelius Miramar AGP Vinyl liner 13,100 gal. Buried 2 ft.
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    JoyfulNoise's Avatar
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    Re: OCLT and FAS-DPD Accuracy Question

    This has been discussed both internally among the TFP experts and mods as well as externally in the threads. It is true that, at higher FC levels the test's reporting accuracy starts to get a little worse than the +/-1 drop tolerance you get when you are below 10 drops of R-0871. But, it should not be that far off that you can't be confident of SLAMs completion. Also, one could wait for the FC to come down a bit and get a better idea of the OCLT at lower FC levels. In 99% of the cases, a person is going to have no overnight loss of chlorine and low CCs fairly quickly in the SLAM process. Achieving clarity is usually the biggest problem faced when trying to complete a SLAM - you'll often see most threads ending with "my OCLT is less than 1ppm and I've had zero CCs since day three of the SLAM but I just can't get the pool clear...."
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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