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Thread: I think my mustard algae from last year came back....

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    new2pools's Avatar
    Join Date
    May 2007
    Hampton Roads/Virginia

    I think my mustard algae from last year came back....

    I had a TIME with it last year and never could get rid of it. I ended up just shocking like crazy, adding algaecide and putting the cover on. Surprisingly when I opened the pool this year, no algae. I fully expected a mess.

    First few weeks all was well.

    Not so, now. I just walked out to check things today and noticed on the shady side of the pool, yellow again on the bottom in streaks like last year. Hubby got in and said it felt slimy. Great. It looks exactly like it did last year. I HATE this stuff. It was such a pain.

    Here are my numbers

    FC 2.5
    CC 0
    PH 7.5
    TA 130
    CYA Less than 20 still

    What should I do? Shock like crazy for 3 days? Put in algaecide of some sort? I do NOT want to have to fight this again for weeks this summer like last year. And I never did get rid of it last year....just gave up.
    27' Round AGP, 17200 GAL, 2 HP/2 SPD Pump/Cartridge Filter.......BBB!

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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: I think my mustard algae from last year came back....

    Well, I did see in another post that with persistent mustard algae you need to maintain higher chlorine levels....with a CYA of 20 you want to maintain at least 3ppm FC in your pool at all times, so if yours drifted below that at any time, with low CYA it's possible if it was hiding anywhere (areas of poor circulation, etc.) it could have survived and start to thrive. It's resistant to regular levels of chlorine. So I'd shock and brush till it's gone and then keep your chlorine a tad higher. Up your CYA a bit and just keep running with higher FC levels, which certainly doesn't hurt.

    Good luck, I know it's a pain when things go wrong!
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner

  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: I think my mustard algae from last year came back....

    The last resort solution for eliminating algae of any type would be to use a phosphate remover. Though it will work, it can get expensive depending on your level of phosphates and rate of introduction of more phosphates. Though you can manage with chlorine alone at higher levels, I did want to at least put out this other option for you.

    Also, if your pool is exposed to sunlight, having a low CYA level may have the FC drop low enough for even regular green algae to grow to consume even more chlorine though not yet be visible. Usually, a pool exposed to sunlight should have at least 30 ppm CYA unless you keep the pool covered most of the time. Then, the mustard/yellow algae prevention level MINIMUM would be 4.6 ppm FC.

    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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