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Thread: FC test seems to be meaningless, I'm about to drown myself!

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    FC test seems to be meaningless, I'm about to drown myself!

    I have been having what seemed like testing inaccuracies for some time now. I figured maybe my methodology is wrong, maybe my measuring is inconsistent, maybe my reagents are bad……

    So I got a speed stir and a sample sizer and new reagents from TFTest Kits and every test gives a different result.
    I thought I must be doing it wrong so I read everything I can find on here and slowed down my drops as well as getting full drops that hang before dropping and being sure the DPD powder is in adequate amounts, etc.

    I got 28 drops, 24 drops 32 drops……

    This is crazy. My head is about to explode. Someone PLEASE tell me what stupid mistake I am making! I would love to be humiliated by my own stupidity, just let me get this testing right!
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    Mod Squad jblizzle's Avatar
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    Are you using a 10ml water sample?
    Are you holding the bottle vertically?

    A variation of 8 drops sure does seem excessive.
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    take one big measuring cup's worth of water out of the pool, mix that up real good in the measuring cup, then do a couple back to back tests with that. It's possible the chemicals in your pool aren't mixed well enough, and every time you dip the thing in the pool you're hitting a different patch of water.
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    Quote Originally Posted by jblizzle View Post
    Are you using a 10ml water sample?
    Are you holding the bottle vertically?

    A variation of 8 drops sure does seem excessive.
    That's Yes, and Yes

    To begin with I was dropping fast. That's when I get 24 drops. Slowed down, measured DPD powder generously, got full hanging drops, and tried to be completely consistent…two tests in a row and got 28 and 32

    - - - Updated - - -

    Quote Originally Posted by BuckeyeChris View Post
    take one big measuring cup's worth of water out of the pool, mix that up real good in the measuring cup, then do a couple back to back tests with that. It's possible the chemicals in your pool aren't mixed well enough, and every time you dip the thing in the pool you're hitting a different patch of water.

    gonna try that now but the pump has been running all day
    25,000 Gal In ground
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    ! Hp No Name Pump K2006 Test Kit

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    Mod Squad kimkats's Avatar
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    The cup/container you are getting the water with...is it used ONLY for getting water out of the pool?

    I was not thinking one day and used the cup I put my chlorine in the pool with to take water out of the pool to test. DUH I wonder why my FC was off the charts! LOL

    Just throwing that out there.

    Kim
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    Mod Squad jblizzle's Avatar
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    I would have though dropping fast would have been more drops not less.

    You should have a drop about every second.
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    OK, here are 6 tests from the same cup. Seems to indicate that the minutest variation can skew the test wildly! As I have been going I am trying to be consistent in all aspects and letting each drop fall off of it's own weight. This seems to be the solution.

    28
    30
    27
    29
    29
    29
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    Mod Squad jblizzle's Avatar
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    I would not call that a wild distribution. The test is good to +/- 1 drop and that is basically what you have.
    Jason, TFP Moderator
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    Quote Originally Posted by jblizzle View Post
    I would not call that a wild distribution. The test is good to +/- 1 drop and that is basically what you have.
    OK, time to take a break and read my Buddhist book "Comfortable with Uncertainty"

    Thanks
    25,000 Gal In ground
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    Scuba_Steve's Avatar
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    Re: FC test seems to be meaningless, I'm about to drown myself!

    In my experience with drop based tests, the higher the number of drops being used, the more inaccuracy.

    Drops are not perfectly uniform. Close, but not perfect.

    If something only requires a few drops to change colors, then this variation probably will not affect the test.

    Your using around 30. If your bottle has a tiny bit of static electricity on the tip it will cause the drops to form slightly small. Over 30 drops you may be off by a couple drops because of this. Or air getting mixed in the drops, or inconsistant squeezing pressure, or etc etc etc...
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