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Thread: Is this algae? Numbers don't seem to support there being any

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    Aug 2013
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    Richmond, VA
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    Is this algae? Numbers don't seem to support there being any

    I've had this showing up in the water for the last four days or so. It's on the bottom of the pool, mostly along ridges in the liner. About 11pm two nights ago, my numbers were these:

    FC: 7.5
    CC: 0.5
    pH: 7.8
    TA: 110
    CH: 80
    CYA: 60 (though I've learned to do the CYA test better since and think this was a little high)

    Based on the CYA of 60, I decided to raise the FC above the shock value of 24. I put in 363oz of 8.25% bleach to raise the FC from 7.5 to 25.5 (went a little high for convenience of dumping in three full 121oz jugs). That was about 11pm that night. I checked the numbers the next day (yesterday) at 11am:

    FC: 24
    CC: 0.5
    pH: 8
    TA: 110
    CH: 80
    CYA: 40

    Not much of a drop in FC or increase in CC. Weird, right? Yet I keep having to vacuum this stuff off the bottom of the pool twice a day. After that test, I added 58oz of 31.45% muriatic acid to drop the pH down (and the TA a little).

    Yesterday was a really sunny day all day, so I expected the FC would drop. This morning at 11am, the numbers are:

    FC: 16.5
    CC: 0
    pH: 7.4
    TA: 100
    CYA: 45

    Yet the pics below are from this morning. Any suggestions?
    Attached Images Attached Images
    13K gallon AG, sand filter, 2.5HP two-speed pump, no shade at all

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    Re: Is this algae? Numbers don't seem to support there being

    Filter Sand? What does it feel like?
    24' round above ground, 13500 gallons, vinyl liner, 18" Sand Filter

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    Smykowski's Avatar
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    Re: Is this algae? Numbers don't seem to support there being

    If it doesn't feel like sand, it's probably a combination of dust and dead algae. Do you have anything in the pool that would be in an area of poor circulation? Stairs, lights, ladders, etc? Is there a solar cover that can have algae living on top of it? Any toys that aren't clean?
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    Re: Is this algae? Numbers don't seem to support there being

    Oh, yeah, I haven't gotten in yet to see what it feels like. But, there doesn't seem to be much/any near the return like I'd think there would be if it was coming out of the filter...and also if I run a brush over it, it disappears rather than just moving around like I'd read sand would. Still, next time it's there (I just vacuumed), I should get in and see what it's like.

    I hadn't thought about just dead algae accumulating, but that would make sense. Yes, there is a set of stairs in the water. No toys or anything...the pool actually has not been used at all since I moved in (two weeks ago) because I've been afraid to have people over until the water is straightened out.

    I should've also added that the color in the pics is pretty close to how it looks - grayish/tanish. Also, my filter pressure is holding steady at 5psi which is always what it's been right after I've backwashed, so no increase there.
    13K gallon AG, sand filter, 2.5HP two-speed pump, no shade at all

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    Re: Is this algae? Numbers don't seem to support there being

    Sure looks and sounds like dead algae to me.

    I would SLAM the pool and I'll bet it goes away in just a few days if you keep your FC up.

    Check under those stairs. Algae loves to find hding places from the chlorine where it can continue to thrive.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Is this algae? Numbers don't seem to support there being

    Thanks guys! I think y'all were right that it was dead algae. I kept all my chemical levels right and vacuumed daily and it diminished over the next few days, and now everything's looked perfect for the last couple of days, and my FC has dropped slowly each day (sun) with 0 CC showing up.
    13K gallon AG, sand filter, 2.5HP two-speed pump, no shade at all

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