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Thread: Always test water with pump running!

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    tcat's Avatar
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    Always test water with pump running!

    I wasn't thinking and tested my FC about 15 minutes after my pump shut off. Got a "1" reading and I panicked, it'd been so good all week. So I turned on the pump and rechecked in 30 minutes, was "6", just what it should be. I was really surprised chlorine settles to bottom that fast. Another lesson learned
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    Re: Always test water with pump running!

    Or maybe the sun "eats" the stuff at the top first? I guess I should start my pump when I test, I usually test when I get home from work and the pump only runs at night.
    ~20,000 gal in-ground plaster pool, 3/4 HP pump, ~3 sqft sand filter (newly replaced May 2013), TF-100 test kit with Speed Stir!

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    Mod Squad jblizzle's Avatar
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    Re: Always test water with pump running!

    Pump should be running for at least 30-60 before any test. And at least an hour after any chemical addition.

    It is annoying that I am not home when the pump runs for solar. So I have to turn it on again in the evening, wait, test, add, wait, turn it off.

    Posted from my Droid with Tapatalk ... sorry if my response is short
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    Re: Always test water with pump running!

    While it's a good idea to test with a well-mixed sample, chlorine does NOT settle to the bottom. It stays in solution and will be distributed evenly throughout the pool. I can't answer why your tests were so different but want to emphasize that chlorine (nor any of the other parameters we test) does not settle to the bottom.
    Dave S.
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    Richard320's Avatar
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    Re: Always test water with pump running!

    Quote Originally Posted by tcat
    I wasn't thinking and tested my FC about 15 minutes after my pump shut off. Got a "1" reading and I panicked, it'd been so good all week. So I turned on the pump and rechecked in 30 minutes, was "6", just what it should be. I was really surprised chlorine settles to bottom that fast. Another lesson learned
    The sun degrades the stuff faster at the top. Maybe you need to stick your arm a little deeper into the pool when you grab a sample?

    I use a 4' piece of " PVC as a pipette to draw a sample from out away from the edge and a couple feet down.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    tcat's Avatar
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    Re: Always test water with pump running!

    I had assumed chlorine was heavier and sank, only explanation I could think of (and I was thinking the liquidator worked on that principle). I use a turkey baster at about 15" deep for each sample. I may try another pump off sample just to see if I can duplicate it tonight. I am using a homemade feeder that dispenses 32 oz. over the 4.5 hour pump cycle. That's why I thought it odd I only got a "1" 15-30 minutes after the pump stopped, should have been at max level for that 24 hour period.
    IG pebble, 15,000 gallon
    48 PentAir DE Filter with backwash valve
    PentAir Whisperflo pump with 1hp 2-speed motor
    Aquabot 4WD, Poolskim
    Intermatic Dual Timeclock with freezeguard
    DIY chlorine feed
    BBB

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    mas985's Avatar
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    Re: Always test water with pump running!

    Chlorine (aqueous) is slightly heavier than water but once mixed with water it doesn't settle out (i.e. separate). The liquidator makes use of this by the way the tank is filled to minimize mixing with the water.
    Mark
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