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Thread: Mustard is back but passing OCLT

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    Join Date
    Jun 2014
    Marietta, GA

    Mustard is back but passing OCLT

    So 2 months ago I was a TFP newbie, and learned a lot (thanks to all). I had a 5 day SLAM, and my water was the clearest I have ever seen it. I figured out my pool was losing about 1-1.5 ppm per day, and I was adding 1/2 gallon of 8.25% daily. Sometimes I would add 1 gallon, every 2 days. All was great until about 2 weeks ago, when I did not add anything for about 5 days. The mustard showed up shortly after. The problem I have is that I am still passing the OCLT. In fact I am more than passing it. Yesterday, I vacuumed about 75% of the yellow off the walls to waste, until I lost so much water, that I had to switch to filter to finish vacuuming. I tested last night at 8 PM, and FC was at 5.5. I added 1 gallon of 8.25% which should have brought it to 7. I just tested now (24 hours later), and I am still at 6, and today was 96 degrees, and very sunny. So I only lost the 1 PPM, that I usually lose in a day.

    So my question is how can I have mustard and still pass the OCLT? Here are my numbers:

    FC: 6
    CC: .5 or less
    CYA: 50
    pH: 7.5
    TA: 70
    27k gal, IG vinyl, Pentair Triton II Sand Filter, 1 HP Hayward Super Pump, Liner 3 yrs old, Intermatic PF1103T Timer w/ Freeze Protection, K-2006.

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    Mod Squad pooldv's Avatar
    Join Date
    Aug 2012
    DFW, TX

    Re: Mustard is back but passing OCLT

    I don't have any experience with mustard algae other than to know that it is persistent and difficult to get rid of.
    More here, Pool School - Mustard Algae
    TFP Moderator
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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Mustard is back but passing OCLT

    So my question is how can I have mustard and still pass the OCLT?
    Circulation. You are allowing the algae to lie still and hide from the chlorine. Brush the algae up into the chlorinated water and the chlorine will kill it and you likely will not pass the OCLT (until the algae is killed)
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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