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Thread: Algae or Dirt??

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    Algae or Dirt??

    Hi, Just registered but have been veiwing for a long time. Very helpfull forum.

    I have a 65,000 litre fiberglass pool with SWG and sand filter, the water is always crystal clear and all levels are ok but has been requiring higher chlorine levels but then again it is extremely hot in australia at the moment.

    I have always had a problem with what i assumed was fine dirt gathering on the bottom of the pool, but the kreepy krauly has kept it clean mostly.
    I have just bought a Zodiac MX8 and noticed it is not picking up this 'dirt' and the 'dirt' seems to be only accumulating on the rough sections of fiberglass and not the smooth sections where it is joined.

    I am thinking this could some form of algae? when i brush it, it seems to dissipate. Or could this be a problem with debris from the filter returing to the pool?

    Thanks for your help in advance.


  2. Back To Top    #2
    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    SW Indiana

    Re: Algae or Dirt??

    Welcome to TFP!

    Algae is a possibility. What are you chlorine and CYA levels?
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

  3. Back To Top    #3

    Re: Algae or Dirt??

    chlorine is 3.0ppm not sure about CYA.

  4. Back To Top    #4

    Join Date
    May 2011
    Clearwater, FL.

    Re: Algae or Dirt??

    Hi ashburgum and welcome to TFP!

    I think that without knowing what your CYA is, how do you know that 3.0 ppm is correct amount to have in your pool to keep enough FC?
    Use this chart for a baseline once you have tested your CYA here:
    The next thing to find out if it is algae, is a overnight FC loss test as outlined in Pool School instructions here:

    Post some pics if you can!
    Swim n Play 21' round, expandable 72" liner, 6FT deep center, buried 14", 12,750 Gallons
    Waterway 1HP-2 speed with 22" Sand filter
    TF-100 test kit
    Thanks to TFP my pool is perfect all the time :party:
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  5. Back To Top    #5

    Re: Algae or Dirt??

    Thanks for the replys,

    CYA is 30.
    Should i shock it now and perform an overnight FC loss?


  6. Back To Top    #6

    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Algae or Dirt??

    Should i shock it now and perform an overnight FC loss?
    I wouldn't just yet. Why not try to determine what it is first? My assumption is the water is warm enough to get in. "pinch" some of the stuff that's settled between your thumb and forefinger. Algae, alive or dead, should be slippery and dirt should feel gritty.

    If that's inconclusive, then I suggest an OCLT. Do you have the correct FAS/DPD test to perform it? If you are not clear on how to do it, reread or ask for help.

    Then, if the OCLT indicates an excessive FC loss, it's time to shock your pool.

    (I doubt this is related to your cleaner, but it is slightly possible)
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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