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Thread: Algae Keeps Coming Back, Even After a SLAM

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    Join Date
    Aug 2013
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    New Bern, NC
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    Algae Keeps Coming Back, Even After a SLAM

    Hi everyone,

    I have an issue that I would like some additional expertise on. I battled this same issue last year as well. To make a long story short, I have had some fine, brownish-green (mostly brown) "stuff" in the the cracks and wrinkles of my pool all summer. It poofs up and disperses into the water when brushed and makes the water cloudy in that local area. I continue to brush and then vacuum this "stuff" to waste. I maintain FC levels using liquid bleach (8.25%) according to the FC/CYA chart from this website. I have always struggled with really knowing if this "stuff" was algae or not. Last week, I had a definite algae issue. I could not see the bottom of the deep end (7ft). I SLAM'ed according to this site, brushed everyday, and vacuumed the piles of dead "stuff" to waste each day. It took about four days and 8-10 gallons of bleach until I got clear water, 0 FC loss overnight, and 0 CC. I thought I was done.

    After the SLAM'ing, I noticed the same "stuff" appear the very next day. The "stuff" does not appear until after I turn the pump on and let it run a few hours. Then I see the "stuff" reappearing on the bottom of the pool. I was confident it was very fine debris coming from the filter (no pollen in the area and just SLAM'ed). And then today I get home from work and the bottom has a slight layer of "stuff" once again. I brush the "stuff" and there is a poof of light green on each brush stroke.

    The part I can't understand is I have not let the FC drop below or even to the minimum of the FC/CYA chart. I checked the FC last night and again this morning (four days after the SLAM) and had zero FC loss overnight. The value was 4.5 ppm and 7.5 pH during the OCLT. (I have been checking the FC each night trying to determine if I have organics or not.)

    Is it possible algae is being introduced to the pool from the filter? Any other ideas? At times, I have not ran the pump to see what happens. When the pump doesn't run, this "stuff" does not appear in the cracks and wrinkles. When I turn the pump for a few hours, the "stuff" is back and continues to accumulate as long as the pump is running

    Pool chemical readings:
    FC - 4.5
    CC - 0.0
    pH - 7.5
    CYA - 30
    CH - 350
    TA - 90

    Thank you for the support. This site is awesome and extremely helpful.
    -Stuart
    In-ground pool, 20k gallons, vinyl liner, sand filter, chlorine sanitizer

  2. Back To Top    #2
    Charlie_R's Avatar
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    May 2013
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    Mexico, MO
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    Re: Algae Keeps Coming Back, Even After a SLAM

    Could it be very fine dust that isn't being captured by the filter?

    When was the last time you did a deep clean on your filter?

    Also, have you tried capturing some of this stuff and checking what it looks like when you try to smear it on a piece of white paper? If it is green when you do that, then yes, algae. If brown, then fine dust.

    For fine dust, you can add some DE to your filter to clean it out of the pool.
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

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    jccams's Avatar
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    May 2010
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    Dexter, MI
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    Re: Algae Keeps Coming Back, Even After a SLAM

    The other thing that comes to mind is your confidence in the CYA level. Is it really 30 or could it be higher and the FC level you are maintaining isn't sufficient.
    24,000 gal vinyl Lazy L, 1 hp pump, DE Filter, Pentair 250K heater, Letro Legend pressure side pool sweep

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    New Bern, NC
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    Re: Algae Keeps Coming Back, Even After a SLAM

    I noticed more green tint to the bottom of the pool when I got home today. It was noticeably green when brushed.

    Charlie_R...I have not deep cleaned the filter as this is my second year of owning the home/pool. However, once I saw additional green in the pool, I removed the valve to deep clean the filter. The water was clear on top at first. But after mixing up the sand good with my hand, the water turned cloudy to green and dirty. See picture. Could this green be some algae living down in the filter and small amounts are pumped into the pool as the pump runs but not when the pump is off? It is feasible IF this algae could be living in the filter. Is this even possible?
    Attachment 31128

    jccams...I am pretty confident in the CYA reading as I tested with a Taylor 2006 and TF-100 test kit. Both had a reading of 30.

    Thanks for the replies.
    In-ground pool, 20k gallons, vinyl liner, sand filter, chlorine sanitizer

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    Charlie_R's Avatar
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    Re: Algae Keeps Coming Back, Even After a SLAM

    Do you have any lights in your pool? If you do, clean behind them, after you start another SLAM.

    I suspect that your FC got below the minimum for your CYA and if there are any traces of algae on pool tools, toys, ladders, and behind lights, or in a channeled filter, that is all it needs to get started again.

    I wouldn't think that there would be any algae living in your filter because it has the same water from your pool, unless it was channeled.

    Adjust your pH, and SLAM again.
    15'x48" 4500 gallon Intex pool, buried 1.5 ft. Pac-Fab Dynamo 3/4 hp pump. Hayward S180T sand filter, bought used. Taylor K-2006 test kit. Rocket mass heater based wood fired pool heater.

  6. Back To Top    #6

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    Aug 2013
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    New Bern, NC
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    Re: Algae Keeps Coming Back, Even After a SLAM

    I was able to pull my light out yesterday and found a good amount of dark green algae living between the light and the housing. I cleaned the housing and started the the SLAM process again. I hope between the algae in the light and deep cleaning the filter that this problem of recurring algae goes away completely. Fingers crossed.

    Again, thanks for the replies.
    In-ground pool, 20k gallons, vinyl liner, sand filter, chlorine sanitizer

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    AimeeH's Avatar
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    Apr 2012
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    Re: Algae Keeps Coming Back, Even After a SLAM

    You might consider elevating to mustard algae shock level. I had a reoccurring algae problem at seemingly normal CL levels until I completed mustard slam. I also discovered algae behind my light housing on the liner upon close inspection.

    First SLAM.....maintaining the CL level until all 3tests pass then elevate to mustard shock level and keep it there for 24 hours.
    18*36*23 true "L" vinyl IG 29,000 gallons. SWG. TF-100 test kit.
    http://tftestkits.net/splash-page.html

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