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Thread: chlorine test inconsistancies

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    chlorine test inconsistancies

    I have been slamming my pool since Friday and have dumped almost 12 gallons of 8.25% bleach in the pool. I have noticed inconsistencies in my FC tests. Just tonight I took two measurements about 10 minutes apart and got a reading 2ppm higher the second time.

    I am extremely careful about holding the bottle the same and getting all the drops to be the sane size. Not sure what to do next.
    15,000 gallon plaster pool with spa and water fall, 250 Pentair MiniMax Plus Heater
    Nautilus FNS FIberglass D.E. Filter 48 Sq ft, Leslie's DPD Complete Chlorine Kit + TFTestkits Chlorine & CCs Kit.
    Oak trees overhanging most of pool

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    UN1017's Avatar
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    Re: chlorine test inconsistancies

    2ppm isn't too bad but I usually don't have discrepancies like that. Just confirm that this is taken from the same water sample and using the same test method and reagents. I noticed you are using two different test kits in your sig...

    What kind of FC numbers are talking about here?
    15'x30' IG - Roman-style - 14K - Pebble Fina Classico
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    Smykowski's Avatar
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    Re: chlorine test inconsistancies

    How long after the dose was test 1 and test 2? Sounds like it may have been mixed in better for test 2.
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    Re: chlorine test inconsistancies

    I am only checking FC and CC with the TFT powder and reagent.

    I took the first sample just a little over an hour after I added chlorine and I took the second one about 10 minutes after that.

    This morning I took three readings. The first two were out of the same bottle, drawn from the pool at the same time and the differed by 2.5 PPM. Then I took a sample with the test tube directly from the pool and it was 3 ppm higher. The third one actually indicated a .5 ppm difference from my measurement last night so I am calling the slam process complete. I will however do another overnight test tonight to confirm.

    Measurements last night about 10 minutes apart were 23.5 and 25.5.

    Measurements this morning 21 and 23.5 taken from the same sample and then 25 taken directly from the pool.

    CC for all of these was at .5 or lower.

    All of these were taken with brand new reagents and powder I just got from TFT on Monday.
    15,000 gallon plaster pool with spa and water fall, 250 Pentair MiniMax Plus Heater
    Nautilus FNS FIberglass D.E. Filter 48 Sq ft, Leslie's DPD Complete Chlorine Kit + TFTestkits Chlorine & CCs Kit.
    Oak trees overhanging most of pool

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    Re: chlorine test inconsistancies

    I wish I could provide a definitive answer for you. I can perform that test within .5 ppm consistently but I have been doing it for almost nine years and I think that may be the difference.

    The endpoint of the test is when you add a drop and there is NO further color change.....then you subtract that drop.

    Are you getting to that endpoint each time?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: chlorine test inconsistancies

    Yes, I am getting to that end point each time.
    15,000 gallon plaster pool with spa and water fall, 250 Pentair MiniMax Plus Heater
    Nautilus FNS FIberglass D.E. Filter 48 Sq ft, Leslie's DPD Complete Chlorine Kit + TFTestkits Chlorine & CCs Kit.
    Oak trees overhanging most of pool

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    Re: chlorine test inconsistancies

    How rapidly are you adding drops? Ideally you let the drops form slowly at the tip of the bottle until the weight overcomes the surface tension, typically about 1 drop per second, with the bottle held perfectly vertically. Any faster than that, or if the bottle is not vertical, your drops can vary in size significantly.

    I usually do about 1 drop every 2/3 of a second, and I get consistent numbers. But with the viscous reagents (the dark ones for the TA and CH tests), it takes me closer to 2 seconds to form a consistently-sized drop.
    25000-gallon semi-public IG concrete/plaster pool, Triton II sand filter
    750-gallon semi-public IG concrete/plaster spa, cartridge filter
    Volunteer pool caretaker for my condominium complex

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    Smykowski's Avatar
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    Re: chlorine test inconsistancies

    Speed very important. Too fast and the drop size is wrong. However, too slow causes problems as well - ever leave the sample on the counter for awhile after the test?
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    Re: chlorine test inconsistancies

    I suspect that the chlorine added to the pool has not mixed completely. Is circulation good in the pool? Are you adding via the skimmer (slowly) or by mixing with water in a bucket and pouring around the pool or by pouring near a return? I would expect that in the short run each of these might give different test results depending on your circulation patterns in the pool.

    I'd guess that best of all would be a few good sweeps with a Wall Whale brush after chemical additions for I observe that this is one heck of a mixer.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: chlorine test inconsistancies

    Quote Originally Posted by TomBorg View Post
    But with the viscous reagents (the dark ones for the TA and CH tests), it takes me closer to 2 seconds to form a consistently-sized drop.
    Drop size does not matter for these 2 reagents (green for TA and purple for CH). In fact you can use more or less drops to see the colors better. Actually the same is true for the pH test as well.
    Jason, TFP Moderator
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    Re: chlorine test inconsistancies

    Could be the rate of my drops. I will try to be more consistent and see what happens. I do hold the bottle vertical typically the first few drops don't come out as slow as the rest. I guess I could waste a few until the air in the bottle stabilizes.

    I have left the sample sitting after finishing a couple of times. Why is this important?
    15,000 gallon plaster pool with spa and water fall, 250 Pentair MiniMax Plus Heater
    Nautilus FNS FIberglass D.E. Filter 48 Sq ft, Leslie's DPD Complete Chlorine Kit + TFTestkits Chlorine & CCs Kit.
    Oak trees overhanging most of pool

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    Mod Squad jblizzle's Avatar
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    Re: chlorine test inconsistancies

    Because it will turn pink again, but the test should be completed before that happens.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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    Re: chlorine test inconsistancies

    I would ensure you are pulling samples from the same location and depth each time. Plunge the rinsed sample bottle, cap off, upside down to elbow depth and turn it upright to fill completely.

    I had some difficulties with consistency when I first started doing my own testing, doubting my drop size, trying to figure out the best swirl/mix technique, etc. Seemed like I needed three hands and someone to count for me. I purchased a speed stir about three weeks into it and was amazed at how easy testing became. I could never go back to hand mixing for the tests.
    Pool: IG 22k- 16x32 clipped corners- vinyl liner, w/ a great board. Built in 3/99, new to me 2/2011.
    Equip: Hayward 3600 DE filter, Hayward CL-200 Chlorinator (empty since 7/5/2013).
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    Located in Cincinnati, OH. TFP lurker since 9/2011, BBB interested since 5/2012 and converted 7/2013.

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    Re: chlorine test inconsistancies

    I say you should make your own control solution, say 5 ppm that way you can know if it's the reagents or technique.
    ~22,000 gallon inground plaster pool, 1 skimmer, 3 return jets
    Irregular pool sized approximately 19' x 40' 9' deep, Color Splash 3G pool light
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    Mod Squad jblizzle's Avatar
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    Re: chlorine test inconsistancies

    Quote Originally Posted by PharmerAnthony View Post
    I say you should make your own control solution, say 5 ppm that way you can know if it's the reagents or technique.
    That is easier said than done.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
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