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Thread: Mustard Algae? How to get rid of it?

  1. #1
    Join Date
    Jun 2006

    Default Mustard Algae? How to get rid of it?

    A week ago I noticed the water started getting agreen tint. I vacuumed and it was a tad better but still greenish and a little murky. I went out of town for 1 week and put in pucks to last the week. I'm back and it's greener and way more murky. I can't see the bottom at the deep end (9 feet).

    I think it's mustard algae - or else lots of sand from a busted filter? when I brush the pool, tons of fine yellowish/brown dust moves around like clouds.

    32K pool
    FC 3ppm
    CC 0
    PH 7.6
    Alk 60
    CYA 80

    Besides dumping in Bleach at 20ppm and keeping in steady until it maintains the level overnight - are there any other things I should do/put in? Or should I use something else instead of bleach? It'll take "tons" of bleach to get to 20ppm and maintaining it for a week or so.

    Thanks in advance!

  2. #2
    mbar's Avatar
    mbar is offline --trial user-- Whizbang Spinner mbar 3 stars mbar 3 stars mbar 3 stars mbar 3 stars
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    Dec 1969
    Ashland, PA

    Default Re: Mustard Algae? How to get rid of it?

    Mustard algae is very difficult to get rid of. Chem Geek did a chart on chlorine levels to fight mustard algae. With a cya of 80, he suggests taking the shock level up to 30ppms, and keepig a minimum of 12ppms chlorine even when it is gone He suggeast a shock level of 60% of the cya level, and minim at 15% of cya level to keep it away once you have it. He also suggest lowereing the ph to 7.2 before shocking which will make the chlorine more effective. He suggest to do this before shocking because high chlorine levels will give a false reading of ph. The only real way to get rid of the mustard algae it to really kill it with very high levels of chlorine, and to keep the chlorine high (15% of cya level) for a long time, because even if a spore of it is left, it will grow again. That's why people think they are getting it back, when in reality it was never really all gone . Hope this helps, feel free to ask any other questions you may have.
    Northeast PA
    16'x32' kidney 16K gal IG fiberglass pool; Bleach; Hayward 200lb sand filter; Hayward pump; 24hrs; Pf200; well; summer: none; winter: mesh; ; PF:7.5

  3. #3
    Join Date
    Jun 2006

    Default Re: Mustard Algae? How to get rid of it?

    Hi mbar - thanks for your input. I did have one more question.

    Does it sound like mustard algae - i.e yellowish/brown clouds of fine dust when brushing the pool? I haven't been able to find any pictures online to make me 100% certain that it's what I'm dealing with. I'm only guessing that it's mustard algae since I've never seen it before. Based on your post...I hope it isn't..


  4. #4
    chem geek is offline PF Supporter Whibble Konker chem geek 4 stars chem geek 4 stars chem geek 4 stars chem geek 4 stars
    Join Date
    Nov 2004

    Default Re: Mustard Algae? How to get rid of it?

    A couple of points. An FC of 3 ppm with a CYA of 80 ppm is not sufficient to keep away algae -- not even green algae (the only exception being with SWG pools which perform more stable chlorine dosing and superchlorination in the SWG cell). With a CYA of 80 ppm, the FC should have been an absolute minimum of 6 ppm.

    As Marie points out, it is very hard to kill mustard algae thoroughly and at a high CYA level it is much easier to dilute the water via a partial drain and refill and to then combat the algae at the lower CYA level. You would probably want a lower CYA level anyway unless you plan on maintaining the higher FC level (see Ben's Best Guess CYA chart). The chart shows a minimum of 5 ppm, but 80 ppm CYA is in the higher end of the 60-90 range which is why I said 6 ppm minimum.

    If you dilute your CYA in half to 40 ppm, then 24 ppm FC should kill the mustard/yellow algae if maintained for several days after no more visible algae is present. A yellow/brown dust is what that algae looks like but pollen can sometimes look like algae. The algae will often start on the shady side of the pool and only algae will be on the walls -- the pollen will usually settle to the bottom. As Marie mentioned, when chlorinating at such a high FC level, even after the partial drain/refill to get to a lower CYA level, it is best to lower the pH (with acid) to 7.2 before adding the chlorine.


  5. #5
    CarlD's Avatar
    CarlD is offline Super Moderator Quark Inspector CarlD 4 stars CarlD 4 stars CarlD 4 stars CarlD 4 stars CarlD 4 stars CarlD 4 stars
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    North Central NJ

    Default Re: Mustard Algae? How to get rid of it?

    In short, there is no short-cut to getting rid of algae. You have to kill it and kill it all, and the ONLY way you do this is by raising your FC level. Bleach is the same as Liquid Chlorine, but pool stores sometimes sell LC at 12-14% levels--so 1 gallon is the same as 2 gals of 6% Bleach. You can use LC as well. You can use the Bleach Calculator to figure how much you need.

    But there's the rule of thumb: 1 gallon of bleach added to 10,000 gallons of water adds EXACTLY its concentration. So 1 gal of 6% adds 6ppm, 1 gal of 5.25% adds 5.25ppm and 1 gal of 12.5% adds 12.5 ppm to 10,000 gallons.

    You need to add two gallons of any of these to 20,000 gallons to get the same increase in ppm.

    So say you have 20,000 gallons in your pool and your ppm is 3. You need a minimum of 17ppm. So if you add 3 gallons of 12.5%, you'll get an increase of 19.5ppm. Or you'll need 6 gallons of 6% bleach for the same effect (increase of 18ppm).

    It's not too hard to figure.

    16'x40' rectangle 19K gal AG vinyl pool; ; Hayward T210 sand filter and 2 Speed Superpump 1hp pump; Solar heated. Test kit: PS 233; PF:6.3; Autopilot SWCG

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