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Thread: Overnight Loss Test - not SLAMing

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    FlyAU98's Avatar
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    Overnight Loss Test - not SLAMing

    I didn't end up doing my water test yesterday until after dark and knew I'd be up by sunrise this morning, so I thought I do an Overnight Loss Test just to see. Upon testing this morning, I had a loss of 1.5ppm (5.5 last night, 4 this morning).

    I was not SLAMing the pool at the time, I just did the test because it was dark.

    Water is Crystal Clear. Pool pump did not run during the night.

    Last night's TF-100 test
    pH=7.5
    FC=5.5
    CC=0
    CH=275
    TA=90
    CYA Not Tested, but its in the 50-60 range (closer to 60), based off testing in the last couple weeks)
    Water temp is in the low 90s.

    Does the loss of 1.5ppm tell me anything? Do I need to SLAM/go to shock level?

    I've got plenty of time to mess with it today...
    15.5K gal, concrete, 1HP AO Smith pump, Hayward C1200 cartridge filter, Zodiac T5 Duo auto cleaner, 8 panel solar heater controlled by Hayward Aqua Solar GL-235

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    Re: Overnight Loss Test - not SLAMing

    Was the pump circulating the water for at least 30 minutes before your morning test? Generally the OCLT needs to be done at shock level, if I remember correctly.
    26' X 52" Intex Ultra Frame. Intex Sand Filter
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    You can lead a horse to (clear) water, but you can't force him to swim in it!

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    FlyAU98's Avatar
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    Re: Overnight Loss Test - not SLAMing

    The pump was NOT on before or during the morning test.
    15.5K gal, concrete, 1HP AO Smith pump, Hayward C1200 cartridge filter, Zodiac T5 Duo auto cleaner, 8 panel solar heater controlled by Hayward Aqua Solar GL-235

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    Re: Overnight Loss Test - not SLAMing

    Pump has to be running and have been running at least 30 mins to believe results.


    http://www.troublefreepool.com/conte...loss-test-oclt
    IG gunite/plaster pool/spa Started 1/17/14, Plastered 5/16/14
    Size: 12'-21'x39' free form, depth ranging from 4' to 7, attached 6 person spa with spillover.
    Equipment: Whisperflo 2hp pump, Pentair 30" sand filter, Pentair Mastertemp 400k BTU heater, 1hp Whisperflo for waterfalls, and a blower for spa floor

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    Overnight Loss Test - not SLAMing

    I've posted on this subject matter before and there are many old threads about this but here it goes again -

    The OCLT criterion were developed as a diagnostic set to be performed at shock chlorine levels. It is not something to be performed on a routine basis at normal Target FC levels because a positive result (chlorine loss of less than 1ppm) doesn't mean anything.

    That being said you had a significant FC loss but no rise in CCs. You could be on the verge of something or, perhaps, some birds were bathing in your pool overnight (stranger creatures find their way into my pool every night!)

    I would simply monitor your FC for a few days and make sure you can hold your water at Target FC levels with your usual amount of bleach additions or SWG % and no serious rise in CCs. As long as you don't dip below minimum FC, your water should be ok.



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    Hemess's Avatar
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    Re: Overnight Loss Test - not SLAMing

    Quote Originally Posted by mrcarcrazy View Post
    Pump has to be running and have been running at least 30 mins to believe results.


    http://www.troublefreepool.com/conte...loss-test-oclt
    The article you linked actually says to turn pump off before testing, and it doesn't say to turn it back on before testing again. Makes sense.
    28,000 IG, gunite, IntelliChlor IC40 SWG with SPA,
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    Re: Overnight Loss Test - not SLAMing

    That says to turn off any pumps, etc. that distribute chlorine sources, not the filter pump. They always recommend your filter or circulation pump is running at least 30 minutes before any of the tests are performed.
    26' X 52" Intex Ultra Frame. Intex Sand Filter
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    You can lead a horse to (clear) water, but you can't force him to swim in it!

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    Mod Squad JVTrain's Avatar
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    Re: Overnight Loss Test - not SLAMing

    Quote Originally Posted by Hemess View Post
    The article you linked actually says to turn pump off before testing, and it doesn't say to turn it back on before testing again. Makes sense.
    The article says turn off SWG when performing OCLT, not the pump. Water should have circulated for 30 minutes to get a representative sample from the pool.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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