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Thread: Black Scum in Skimmer

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    Join Date
    Nov 2010
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    Fort Erie, ON
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    16

    Black Scum in Skimmer

    This year, I noticed that there was a black, oily scum in my skimmer. Is this likely from atmospheric pollution or is it from something in my pool's chemistry?
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    19x35 Grecian In-Ground Pool
    Jandy FloPro FHPM 1.0-2CND 1.0 hp 2-speed pump
    Jandy CV460 cartridge filter
    Waterway ClearWater chlorinator

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    Mod Squad Bama Rambler's Avatar
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    Jun 2009
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    Re: Black Scum in Skimmer

    It's most likely atmospheric, but do you have a full set of test results?
    It would also help if you would tell us the chems you've added to your pool.
    Do the swimmers wear a lot of sunscreen/
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp 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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    Mod Squad woodyp's Avatar
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    Re: Black Scum in Skimmer

    suntan oil and dirt most likely. Mr. Clean eraser will fix it.
    16x32x52" Steel Cornelius Miramar AGP Vinyl liner 13,100 gal. Buried 2 ft.
    2 Speed Hayward Power-Flo Matrix 85 g.p.m. 22" 250lb. sand filter hard plumbed
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    Join Date
    Jun 2013
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    East TN
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    Re: Black Scum in Skimmer

    Alot of people have that in their skimmer. I dont believe its sunscreen or anything like that on my end because no one has used our pool in months, mainly because of the rainy weather we've had and I still get it. Not saying it cant come from sunscreen. I saw somewhere it could be the ink from the vinyl liner wearing off. So I really dont know where mine comes from. If you wait until night time with the pump running for awhile, take a bright flashlight and shine it down in the skimmer. You will see the oil on the top layer of water. The oil doesnt get sucked down the pipe since its the top layer and it cant go back out of the weir so its stuck there. The oil seems to build up into a grease that sticks to the sides. I usually take a rag and sop up the top layer the best I can to get the oil out and then clean the grease off the sides.
    18,000 Gallon Aboveground. Sand Filter with 2HP 2 speed Pump.

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    Mar 2007
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    San Rafael, CA USA
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    Re: Black Scum in Skimmer

    A scum ball can be used to collect the grease so that it does not collect as much on skimmer surfaces.
    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
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    Join Date
    Nov 2010
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    Fort Erie, ON
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    Re: Black Scum in Skimmer

    I think that very little suntan lotion has been washing off from the swimmers. My wife and I usually just go for a swim after getting home from work and we've only had 2 pool parties this summer and I don't think anyone used lotion on those days.

    I just use an old j-cloth to wipe the skimmer and I scrub the thermometer with a brush and soapy water. I try to wash out the cloth with laundry detergent afterwards but the residue doesn't come out easily.

    My latest pool store chemical report shows the following:

    Free Chlorine - 4.5 ppm
    Total Chlorine - 4.5 ppm
    Combined Chlorine - 0 ppm
    pH - 7.4
    Adjusted pH - 7.4
    Total Alkalinity - 115 ppm
    Adjusted Alkalinity - 115 ppm
    Stabilizer - 60 ppm (IIRC - measured with reagent and sight glass)

    In the spring, I dumped a ship-load of chlorine in the pool to kill the algae. After the water finally became clear, I added granular stabilizer through the skimmer. To prevent algae growth, I've been adding 250 mL of PolyQuat 60 every week, usually the day before shocking the pool with 10L of 12% chlorine.

    I've also had to add several 4 kg pails of Alka-Plus and a couple of 8 kg pails of Calcium Chloride. That probably has something to do with the trichlor tablets I've being using for chlorine dosing.

    On another topic about Chlorinator Residue, the gummy residue I've been finding this summer may be a result of stearates possibly being in the trichlor tablets.
    19x35 Grecian In-Ground Pool
    Jandy FloPro FHPM 1.0-2CND 1.0 hp 2-speed pump
    Jandy CV460 cartridge filter
    Waterway ClearWater chlorinator

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