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Thread: OTO Vs FAS/DPD tests

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    OTO Vs FAS/DPD tests

    I understand what they do... but if your test using the OTO then do a further test using FAS/DPD shouldn't the values match?

    I'm using the TF 100 (test in the blue box) to test pH and chlorine daily and then once a week I'm doing the full battery of test TA CH etc....

    Should not the results from the FAS/DPD which gives me.... FC + CC = TC equal the total value I measured using the quick test? Or am I missing something.

    I realize the OTO is a ball park measurement... but sometimes their not even close.

    Also.. when doing any titration test (looking for a color change..) when is the test over.. when I get as much as a blush of the color Im looking for.. or a strong color change? ie if Im looking for pink... and the color turns to "pinkish" is that enough or should I keep adding drops until I get a "strong pink"
    Escondido Ca [*]~23000 gallon plaster pool built in the 70's[*]Pentair VF Pump running 10hrs at 1800rpm getting and estimated 35-40 GPM thruput[*]Sta-Rite Cartridge filter

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    Richard320's Avatar
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    Re: OTO Vs FAS/DPD tests

    Quote Originally Posted by BitViper
    I understand what they do... but if your test using the OTO then do a further test using FAS/DPD shouldn't the values match?

    I'm using the TF 100 (test in the blue box) to test pH and chlorine daily and then once a week I'm doing the full battery of test TA CH etc....

    Should not the results from the FAS/DPD which gives me.... FC + CC = TC equal the total value I measured using the quick test? Or am I missing something.

    I realize the OTO is a ball park measurement... but sometimes their not even close.
    In a perfect world, yes. In reality, no. I know from my own comparisons that anything between 4 and 7 FC looks like 5 on the OTO test.
    Also.. when doing any titration test (looking for a color change..) when is the test over.. when I get as much as a blush of the color Im looking for.. or a strong color change? ie if Im looking for pink... and the color turns to "pinkish" is that enough or should I keep adding drops until I get a "strong pink"
    On the FAS-DPD test, it's when it goes clear - completely clear, as if it was just pool water. The other tests, you keep counting until the drop that makes no difference, then subtract 1. Just for demonstration: If TA = 80, the first 5 drops do nothing. 6 goes grey. 7 turns pale pink. 8 goes barbie pink. 9 makes no difference to the color. The last drop to make a change was 8, so TA = 80.
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    Mod Squad Bama Rambler's Avatar
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    Re: OTO Vs FAS/DPD tests

    On the FAS-DPD you're looking to go from pink to completely clear. You add enough powder for it to go pink. A little too much won't hurt anything. Then add the R-870 drop by drop until it turns completely clear. As Richard said, in a perfect world they should be pretty close but in the real world they quite often aren't.
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    Isaac-1's Avatar
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    Re: OTO Vs FAS/DPD tests

    Also you need to make sure your holding the dropper correctly
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    Re: OTO Vs FAS/DPD tests

    FAS-DPD you're looking to go from pink to completely clear
    exactly.. I was more concerned with changes in color.. but your correct...

    Great explication Richard.... Its not just the color change.. but when changes stop
    Escondido Ca [*]~23000 gallon plaster pool built in the 70's[*]Pentair VF Pump running 10hrs at 1800rpm getting and estimated 35-40 GPM thruput[*]Sta-Rite Cartridge filter

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