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Thread: Yellow spots on bottom of pool

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    Yellow spots on bottom of pool

    Well I just got the house and Jason helped me get everything cleaned up and running well using the BBB method. We have been swimming about every other day and when I take the solar cover off the pool is crystal clear but the bottom is spotted with yellow spots.

    It isn't sand, or dirt and you kind of have to brush it to get it to come off the bottom. If you just swirl the water around it, it won't move. When you do brush it, it kind of clouds then vanishes.
    The spots are mostly the size of a dime but some are the size of a fifty cent piece. I would say there are 30 spots or so every other day.

    Is this possible mustard algae, I was reading that it was pretty rare to get so I didn't want to jump to conclusions.

    Water temp is about 78 degrees

    CYA 30-35
    FC is typically around the 3-4 level (I bring it to 7 and by day two it will be 2.5 or 3 then we swim and I bring it back to 7
    TA is 110
    pH is 7.5
    CC is 0
    CH is 120

    Pump has new sand and runs about 14hrs a day on a timer.

  2. Back To Top    #2

    Join Date
    Feb 2008
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    Denton, TX
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    5,061

    Re: Yellow spots on bottom of pool

    Could be algae. Have you tried doing an overnight FC loss test?

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    duraleigh's Avatar
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    Sebring, Florida
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    Re: Yellow spots on bottom of pool

    Mustard algae typically clings to pool walls and is more of a very light coating that brushes off quite easily. However, there are over 7,000 species of algae, I think, and it sure sounds like that might be one of them.

    Your numbers look good so the next step, as 257 indicates, is the overnight free chlorine loss test. Post up if it's not clear how to perform it and we'll all help.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Yellow spots on bottom of pool

    Just took my FC / CC so I'll report in the morning.
    I'm familiar with the overnight test. Had to convert from Bac to bleach have done way too many FC tests in the last 6 weeks. Have the TF100.

    Currently
    FC 8.5
    CC .25 (This is normally 0)

    Thanks for the suggestion, I didn't think to check that.

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    Re: Yellow spots on bottom of pool

    Last night I was at 8.5 FC this morning when I got up the sun had been on the pool for about an hour and I'm at 7.5 FC.

    What do you all think?

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    Join Date
    Feb 2008
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    Re: Yellow spots on bottom of pool

    Quote Originally Posted by someotherguy
    Last night I was at 8.5 FC this morning when I got up the sun had been on the pool for about an hour and I'm at 7.5 FC.

    What do you all think?
    I'd say that it passed the test.

  7. Back To Top    #7

    Re: Yellow spots on bottom of pool

    So what do you think that it is? I'm going on vacation so I'm going to have to have someone else add the bleach (and I'm sure they will just dump some in each day) What a great time for stuff to be showing up in the pool.

    If I wanted to bring it to 24FC (mustard shock for my CYA level I think) how long can I leave it there, would it be ok if the person dumping the bleach in every other day or so kept bringing it back to 24 or do you not want it to be at 24 for that long in case of damaging something?

    Just trying to figure out what level I should have them keep it at while I'm gone so I don't come back from vacation to a huge mess.

  8. Back To Top    #8

    Re: Yellow spots on bottom of pool

    Here is a gallery link of pool / spots.
    https://www.dropbox.com/gallery/2594099 ... l?h=94c55d

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    Join Date
    Feb 2008
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    Re: Yellow spots on bottom of pool

    My next step would be to shock at the mustard algae level and see if that made a difference. It can be at 24 for as long as you need it there.

  10. Back To Top    #10

    Join Date
    Jun 2011
    Location
    Waldorf, MD
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    Re: Yellow spots on bottom of pool

    I have got the same issue.

    It all started when the pool got extremely cloudy thought it was just bad filtration until the filter got clogged very fast. I shocked the pool and everything turned out great. 1 week later.. the same cloudiness comeback. I repeated the shock, 1 week it did not come back but I started to see a lot of those tan spots like your pictures show.

    The last two times I shocked it I noticed after shocking that tan spots started to show up all over the floor. I threw it off as dead algae falling out and just vacuumed it. However even the last shock (I doubled the dose of what I normally shock this time)I notice some spots still keep coming back in the same spot. Its not all over the pool anymore this time just a for key spots.

    After reading and reading I figured it was mustard algae. However I sometimes doubt this because:

    1. It does not really feel slimy, it does a bit but mostly feels like.. sand.
    2. Even with the high FC levels and scrubbing and following mustard algae procedure it still comes back. (leaving the pole and brush in the water and scrubbing at least twice a day, I run the robot 24 hrs along with the filter and maintain FC levels).
    3. My FC barley changes overnight and I never have any CC
    4. Mustard Algae is rare and nobody has ever described it as sand like patches on the pool floor. It said to grown in shady areas of the pool.

    If this latest shock does not work, I am really clueless at what it is and how to get rid of it. Its costing me a ton in pool shock though.

    Edit: I shocked at Mustard algae levels and this has not gone, My next guess is a leak that is putting sand into the pool. The bucket test is showing 1/2 inch loss in the pool and 1/4th loss in the bucket. So perhaps the leak is putting sand into the pool.

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