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Thread: Mustard Algae - Please help!!

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    Mustard Algae - Please help!!

    My husband and I are new pool owners (bought the house in June) and we are now having problems with mustard algae. In July we had horrible nitrate problems but after draining, refilling and adding tons of chlorine, we got it under control (hundreds of dollars later). During this time, the pool store employees never gave us consistent information and now we doubt their advice. With that being said, we need help getting rid of this yellow algae. For the past week I've scrubbed and vacuumed almost every day. One day the pool will look great and I'll think I've taken care of it and the next morning there will be yellow/brown stuff on the floor and walls. My pool stats are below. The pool store said we should add 2 lbs of Yellow Out, wait 5 minutes and add 2 lbs of Power Powder Plus, wait 12 hours and add 1 lb of Power Powder Plus and then wait 12 hours and add another 1 lb of Power Powder Plus. At this point the algae should be dead and we'll need to add a clarifier. Like I said we've gotten such bad advice before and I'm hesitant to listen to them now. Would this method that they suggest take care of our problem? Any help and advice would be great.

    16K Above ground pool - sand filter
    FC - 1
    TC - 3
    PH - 7.8
    TA - 70
    CH - 220
    CYA - 100
    Phosphates - 200
    16K AG, sand filter.

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    dmanb2b's Avatar
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    Re: Mustard Algae - Please help!!

    Welcome to TFP...I'd suggest not following that advice. You'd be better served investing in a good test kit and then shocking the pool to mustard algae level. Given it's MA and you'll need frequent testing I'd suggest getting the TF100XL from tftestkits.net or the Taylor K2006C. Once you have the kit, we'll be able to help you get rid of the MA issue
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

    Pool School, TFTestKits, Pool Calculator

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    Re: Mustard Algae - Please help!!

    Jennifer,
    Welcome to the forum In addition to dman's advice, I will comment on why you have mustard algae.

    Your CYA is simply too high. A CYA of 100 requires FC to be kept above 7 all the time or you are susceptible to develop algae as you have. Pool stores (most of them, anyway) do not understand this CYA/FC relationship so they never understand just how high you must maintain your FC to keep the algae out.

    If you haven't found Pool School yet, it's in the upper right hand corner of each page....read the "ABC's of Pool Water Chemistry" . It'll get you off to a good start to understanding and will probably prompt you to ask a lot of questions.....that's good....we'll all help.

    I didn't see which part of the country you are in so I don't know how much swimming you have left. Let us know that as that will alter the advice we give.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Mustard Algae - Please help!!

    Thanks for your replies. I live in Atlanta and have maybe a couple of weeks left to swim. I don't know if it would be a good idea to close the pool for the winter without taking care of the yellow algae first. After doing a little more research on the website and reading other forums, I decided to try to partially drain the pool (1/3) at a time to get the CYA down and then tackle the algae by super chlorinating it. Should I shock it tomorrow morning or wait until the evening? Also, should I just shock it once at the MA level or do I need to maintain that level for a period of time?

    Duraleigh - I agree that the pool store people do not know a lot about CYA/FC relationship because when I asked her if the CYA was too high at 100 she said no and that it was okay. She also said that she didn't have a lot of knowledge about CYA and she should probably learn more. That made me question everything she told me thereafter . She also mentioned that I had a "chlorine lock". I don't know what that is but will super chlorinating it (to MA level) take care of it?


    Any help and advice on what steps I need to take after partially draining and refilling the pool would be awesome.
    16K AG, sand filter.

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    Mod Squad Bama Rambler's Avatar
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    Re: Mustard Algae - Please help!!

    I'll add my welcome too.

    The first thing I see is that your CC is 2 which means you need to shock. Shock is a process and not a product as the pool stores would have you believe.

    Since you only have a couple more weeks to swim, here's what I would do.
    1. Order a good test kit[/*:m:3litursi]
    2. Learn to use the Pool Calculator if you haven't already.[/*:m:3litursi]
    3. Add enough MA (Muriatic Acid) to bring your pH to 7.2 That's 1 quart.[/*:m:3litursi]
    4. Add enough liquid chlorine to get to shock level. That's 4½ large (182oz) jugs.[/*:m:3litursi]
    5. Take a sample to the pool store and have them test it. Don't buy anything they recommend but come back here and post the numbers.[/*:m:3litursi]


    1 & 2 are the best things you can do for yourself and your pool. You can stop relying on the pool store and they're highly suspect numbers. pH they usually get pretty close but everything else is hit or miss and CYA is rarely correct.

    We can help you with your pool and next year if you follow our advice you'll have a truely Troublefree Pool.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Mustard Algae - Please help!!

    If the CYA level is truly as high as reported, then it might be better to do a partial drain/refill to lower it since it will take less chlorine to kill off the algae if the CYA is lower -- and the CYA will need to get lowered eventually anyway.
    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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    Re: Mustard Algae - Please help!!

    Thanks to everyone for their help. After doing a partial drain and refill on Friday/Saturday, my cya is at a 40. I shocked the pool on Sunday to the MA level and then noticed that on Tuesday the pool was looking better but there were still yellow spots. So I brushed and vacuumend the pool and then shocked it again to the MA level (chlorine level had dropped slightly). When I got home today the pool is looking awesome with no yellow spots anywhere.All the other chemical levels are okay (my pH was a little weird but I think that's because of the high chlorine levels). All I'm left with is white dust (which I think is dead algae??). I backwashed the filter and brushed the pool. Should I continue to vacuum the pool to get rid of the white dust or will be okay to just brush and let the filter take care of it? Also, we want to close the pool in the next week or so, would it be okay now that we think we are rid of the MA?
    16K AG, sand filter.

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    Re: Mustard Algae - Please help!!

    Mine is crazy with white dust. I'm letting the pump take care of mine, no issues so far.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    dmanb2b's Avatar
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    Re: Mustard Algae - Please help!!

    As long as you can pass the overnight FC loss test and your CC is 0.5 or less, you should be good to go as far as closing is concerned. Good Job
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

    Pool School, TFTestKits, Pool Calculator

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