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Thread: Mustard algae gone

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    Noorm's Avatar
    Join Date
    Apr 2015
    San Jose, CA

    Mustard algae gone

    After a few weeks of trying to get CYA down so I could slam at a reasonable FC, I spoke with Cholrox people (1-800-SOS POOL).
    They informed me that CYA was not really a problem, that mustard algae is chlorine resistant, and suggested using XTRABLUE algaecide. Over night my algae is nearly gone.
    I highly recommend this product. I'm kind of surprised that I have seen no mention of algaecides in my previous threads regarding this problem.

    By the way, the BIOactive CYA reducer was not effective for me. I could have saved that $50 if I'd talked to these folks first. In all fairness to the forum, the consensus was pretty negative on the BIOactive stuff, but I thought it was important to get the cya down so I tried it as a last resort.
    In ground concrete/plaster. Re-plastered 5 years ago Approx 30,000 Gal.
    Hayward 2 speed pump and C3030 cartridge filter. Taylor K-2006 test kit

  2. Back To Top    #2

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Mustard algae gone

    Yellow/mustard algae is more resistant to chlorine, but it can most certainly be killed by chlorine. It's about twice as resistant as regular green algae so if one doesn't completely get rid of it then it requires maintaining roughly double the minimum FC/CYA levels in the Chlorine / CYA Chart to prevent its growth. This chart shows this minimum and also the higher SLAM level to kill off yellow/mustard algae. One needs to get behind light niches and make sure to completely eliminate the algae (see the Pool School article Mustard Algae).

    As noted in this MSDS, the Clorox Pool & Spa Algaecide Xtra Blue is 3.3% copper. Copper is an effective algaecide, but it has a serious downside of staining pool surfaces, particularly plaster surfaces. This is more likely to occur when the copper concentration gets higher or the pH gets higher. So you should be careful the next time you shock your pool with a hypochlorite source of chlorine since that will raise the pH and may stain your plaster from the copper now in the water.

    There are other algaecides promoted by the pool industry to work around high CYA levels including the use of sodium bromide that essentially turns the pool into a bromine pool (bromine is not reduced in its active level by CYA) or the use of ammonia to form monochloramine (again, not reduced in its active level by CYA). However, the better solution is to lower the CYA level so that chlorine can be more effective. Otherwise you end up staying on the endless trendmill of using algaecide products, some of which have side effects (such as staining from copper).

    The only way to remove the copper in your pool is to dilute it with a drain/refill or to use an expensive metal removal product such as CuLator (which has had mixed results on this forum).

    If you were unable to get rid of the yellow/mustard algae through an elevated SLAM exposing darker areas of water with low circulation to elevated chlorine levels, then a better algaecide-like approach would have been to use a phosphate remover since it would not have any side effects except being costly. It is unclear whether the use of 50 ppm Borates or the use of a weekly Polyquat algaecide would be effective against yellow/mustard algae -- they are certainly effective against green algae but of course chlorine alone at the proper FC/CYA level easily prevents such algae growth so such products are not necessary.

    This is why we say never to mix pool store (or Clorox) advice with ours.
    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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