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Thread: Mustard Algae - newbie

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    Mustard Algae - newbie

    Hi folks, I have been attempting this BBB method this year and have saved so much money and have stayed pretty trouble free with our pool - best season ever! I have not mastered this yet, but as I said, it is much much improved.
    We had several days of rain and I did not maintain so now I have an algae issue. Honestly, I don't know if it's mustard or not. I have had plenty of green algae and this appears different. It is more brown in color, and when disturbed puffs away in a cloud. We have shocked and vacuumed and it comes back the next day. Typically it is more on the bottom and seems to be settling in the crevices... maybe it's dead algae?? I will do overnight test tonight.
    Here are my numbers today:
    FC: 1.6
    CC: .1
    ph: 7.9
    CH: 140
    TA: 86
    CYA: 80

    Any advice would be appreciated. The cya level is from last year; it has come down some as we have replaced water little by little. We have not added any trichlor or dichlor product this season. My hubby isn't convinced about bleach so we have been using cal-hypo 63%. I don't think that adds cya, right?? Last year we opened a green swamp (2nd year owning house with pool) and we put in 30 gallons of bleach or more and saw no result so he didn't believe it worked! I don't know what we did wrong... anyway, i digress... where do we go from here? What numbers need adjusted at this point and should we shock to mustard algae level??
    Thanks for any help!!

    26,000 IG, vinyl liner
    18x36 IG concrete w/ vinyl liner - 28,000 gal; 1hp Hayward SP w/ sand filter.

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    Join Date
    Jun 2007
    Long Island, NY

    Re: Mustard Algae - newbie

    1st thing you should do is re-test your CYA. You say that number is from last year. We need to know the number now as that will make a huge difference in the chlorine levels you need to maintain on a regular basis as well as the shock levels. As an example: If your CYA is 80 then you would need to maintain a minimum FC of 5.8. That is higher then shock level a CYA level of 10. Not a safe number to swim in.

    So any advice on chlorine levels without knowing the CYA level is a guess at best.

    You also need a good test kit. From your reported levels I am assuming you are taking your water to a pool store. Most of us here use the TF100 test kit you can get from

    I do not use cal-hypo 63% so I know next to nothing about it.

    From your post you need to shock and maintain the shock level until the water is clear and your overnight tests indicate less than 1ppm loss of FC with a CC level of 1 or less. You also need to keep your filter running 24/7 during the shock phase.

    Be sure to read everything in Pool School, particularly Defeating Algae

    As for why the bleach did not work on the green swamp, with a CYA of 80 you need over 14 gallons of 6% bleach just to reach the shock level of 32. To maintain that level for days could consume more than 30 gallons easily.
    18' round x 52" vinyl AGP holding aprox. 7633 gallons of crystal clear sparkling water, most of the time. Hayward s166t sand filter, 1 hp pump and 2-2x20 Fafco panels is parallel. TF100 test kit and BBB!

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    Re: Mustard Algae - newbie

    The cya is current. What I meant was the level is high from the chems used last year. 80 is the current cya. And we do run our pump 24/7 anyway.
    18x36 IG concrete w/ vinyl liner - 28,000 gal; 1hp Hayward SP w/ sand filter.

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Mustard Algae - newbie

    So with a CYA of 80, You should be keeping your chlorine steadily up around 8ppm.....all the time.

    To get rid of the algae you need to bring it up around 30+ and hold it there until your pool clears.

    That may be 4-5times as much chlorine as you have ever used but that's how you get rid of the algae and keep it away. Unless you commit to those high levels, you will continue to use excess chlorine and fight algae for the rest of the season.

    Additionally, as Macrosill suggests, you need your own test kit. BBB is not any special or magic formula. It is accurately testing your own water and understanding what to do with the test results.

    Read how to shock your pool in pool school. You have not shocked properly which is why the algae keeps coming back.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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