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Thread: Crystal Clear but failing OCLT

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    Crystal Clear but failing OCLT

    TF-100 Readings this morning:

    CYA=55
    TA=70
    pH=7.7
    CH=180
    TC=17.5 (Last night was 19.0)
    FC=17.5 (Last night was 18.5)

    I noticed a very slight haze to the pool after our July 4th party (about 15 swimmers in 90 degree water). So I brought the pool to shock level and have pretty much maintained it there for 4 days while doing OCLT each day. The water is now sparkling clear (was on day 1 after shocking) and CC always reads 0.0 or 0.5. However the OCLT usually shows an FC loss of either 1.0 or 1.5 ppm (one reading was even 2.0).

    Is it possible that after 4 days of shocking and low CC levels and sparkling water that I still have organics? Or is there possibly something else going on?

    By the way, we've been swimming at shock level (but not at night so no interference with OCLT). I assume that is ok.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Mod Squad zea3's Avatar
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    Re: Crystal Clear but failing OCLT

    Have you brushed the pool while it is at shock level? Cleaned any light niches? Was the sun completely off the pool when you pulled samples for your OCLT?
    TFP Moderator
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    Re: Crystal Clear but failing OCLT

    +1 what zea3 said.
    we've been swimming at shock level (but not at night so no interference with OCLT). I assume that is ok.
    It sure is.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Crystal Clear but failing OCLT

    I've been running my polaris sweeper along with occasional brushing. No light niches or ladders in the pool.

    I take the OCLT at 7:00pm and 6:00am. No sun on the pool during those hours.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Butterfly's Avatar
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    Re: Crystal Clear but failing OCLT

    I suggest you raise the shock level to about 24.
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

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    Re: Crystal Clear but failing OCLT

    One more piece of info.

    I have not been running my pump during the OCLT or the SLAMing process (although I did run it 24x7 the first day of SLAMing until it was crystal clear). Since then, I only run the pump from 6:00am to about 6:00pm daily. So I am taking OCLT samples while the pump is off.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Re: Crystal Clear but failing OCLT

    It probably doesn't make too much difference but I think I would run the pump during OCLT. Keeping your pool water well mixed always gives the most accurate results and this test requires good precision.

    You're close, but the test results indicate the need to continue for a bit more. I also like BF's suggestion to go to 24 ppm....that just might do the trick.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Crystal Clear but failing OCLT

    Just did a quick re-read of the SLAMing process, I realized that last night, I only had FC loss of 1.0ppm.

    According to the process, I have now passed all 3 tests.

    1) Crystal Clear water
    2) CC at 0.5 or less
    3) OCLT is 1.0ppm or less

    Does this mean I'm done? I'd really like to see less FC loss overnight though.

    Here is why........

    Target FC for SWG = 3.0ppm
    I run my SWG at 65% for 12 hours and that produces 2.25 ppm per day (according to pool calculator)
    Assume FC loss of 1.5-2.0ppm on most days
    if I continue to lose 1.0ppm during the night, I have a daily loss of 2.5-3.0 ppm.

    Therefore, my SWG will not keep up with the FC loss with overnight loss of 1.0ppm. Of course unless I run my SWG longer or higher percentage. Never had to do that in prior years though.

    Does this math makes sense? I realize there is some margin of error in the calculations but I've been noticing that my SWG has not been keeping up and I expect that it's due to a higher amount of daily FC loss than usual.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Re: Crystal Clear but failing OCLT

    Quote Originally Posted by Butterfly
    I suggest you raise the shock level to about 24.
    I can certainly try that. What's a couple more gallons of bleach

    However, I'm not sure it's safe to swim above shock levels. I've always considered it safe to swim at or below shock. Perhaps I can get it to 24 and kill it quickly to minimize downtime.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Re: Crystal Clear but failing OCLT

    Your thinking makes sense but I think you will see your overall FC loss drop now that you have cleared the organics.

    I would suggest you declare victory and let your FC come down to normal levels but don't change ANY settings and observe how your FC holds up.

    Obtaining less than 1.0 ppm FC loss overnight is pretty darn tough to do consistently.....you may frustrate yourself trying for that.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Crystal Clear but failing OCLT

    OK, that's good news. For some reason I was thinking I had to consistently attain 0.5 FC loss in OCLT. Maybe I just need to turn up my SWG to 80% during the warmer weather (but I won't change that until I observe how FC is holding up). At first I was thinking my SWG was dying but I ran an overnight SWG test and calculated (using pool calculator) it was producing exactly the amount it was rated for (1.38lb/24hr).

    After the July 4th pool party, there were a couple OCLT's that resulted in 1.5 FC loss, so I think the SLAMing was called for.


    Thanks to everyone here for all the help. Even though I understand the process, it's always nice to have that vote of confidence from TFP folks!!!
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    Re: Crystal Clear but failing OCLT

    Quote Originally Posted by Butterfly
    I suggest you raise the shock level to about 24.
    Sorry, I misread your test results! (thought I read that OCLT was 1.5)

    And yes, you do seem to be good to go! Nice work
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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    Re: Crystal Clear but failing OCLT

    Quote Originally Posted by Butterfly
    Quote Originally Posted by Butterfly
    I suggest you raise the shock level to about 24.
    Sorry, I misread your test results! (thought I read that OCLT was 1.5)

    And yes, you do seem to be good to go! Nice work
    No problem! Most of my OCLT results were 1.5 until last night (which was 1.0). I can see how my post was a little confusing.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    techguy's Avatar
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    Re: Crystal Clear but failing OCLT

    If most of you OCLT tests for the past week have been 1.5 and you are hazy, you are on the edge of a bloom and its time to SLAM it hard until you hold your OCLT to less than 0.5 and your FC loss to 1.0 or less.
    -- Guy --
    10K gallons in 21' Round 52 inch wall Aqualeader AG, Hayward Power Flow LX 1.5 HP pump motor, Hayward Perflex EC50AC DE filter w/Cellulose, Wide mouth skimmer, 2013 new Diver Dan (craigslist) to replace the faded old Hayward AquaBug. TF-100

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    Re: Crystal Clear but failing OCLT

    Quote Originally Posted by techguy
    If most of you OCLT tests for the past week have been 1.5 and you are hazy, you are on the edge of a bloom and its time to SLAM it hard until you hold your OCLT to less than 0.5 and your FC loss to 1.0 or less.
    Agree. I've been SLAMing for 4 days and water is now sparkling, CC is 0.5 and OCLT was 1.0 last night. I was concerned about the 1.0 OCLT but others here say that is good enough given my CC and water clarity.
    TF-100 Test kit, 24,000 gal. free form Vinyl. mybluepool AC-600 SWG, STA-RITE S7MD60 DE filter, 3/4 HP STA-RITE MPRA6D pump, Polaris 280 w/booster, Raypack Propane heater, Looplock mesh cover; All located in New England.

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    techguy's Avatar
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    Re: Crystal Clear but failing OCLT

    OK, sounds good. It may have been my reading but it sounded as if you were still hazy. It sounds like Butterfly and Duraleigh have you under control.

    I like Butterfly's suggestion of one last FC bump to clear out any lingering algae. It could get you clear and sparkly with an easy OCLT pass.
    -- Guy --
    10K gallons in 21' Round 52 inch wall Aqualeader AG, Hayward Power Flow LX 1.5 HP pump motor, Hayward Perflex EC50AC DE filter w/Cellulose, Wide mouth skimmer, 2013 new Diver Dan (craigslist) to replace the faded old Hayward AquaBug. TF-100

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