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Thread: Calcium scaling or black algae

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    Calcium scaling or black algae

    New to the forum, but I have been reading most of the basics, and trying to come up to speed.

    I am seeing a strange dark stain at various parts of my pebble-tec pool. Thought it was black algae, but after looking at posts ont his forum, I thought that this was probably not the same thing. However, I was already taking steps to combat black algae, so I am in the midst of shocking the pool and scrubbing the dark areas. I saw pictures of calcium scaling and thought that might be what is actually going on.

    Here is a picture:
    [attachment=0:3j2exj10]Pool staining 2.gif[/attachment:3j2exj10]

    Did measurements on the pool using the TF100.

    FC: 6.5
    CC: 0.5
    pH: 7.2
    TA: 110
    CYA: 25
    CH: 1100 (Wow!)

    I didn't do measure the CH until today (after shocking for 3 days), after reading about the scaling.

    So any ideas? Is this scaling? Everything else looks good on the pool except for this dark discoloration (or is it bleaching of the other areas).

    Thanks for any help.
    Attached Images Attached Images
    20k gal., Pebble-tec, SWG, 60 gal pentair DE

  2. Back To Top    #2

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

    Re: Calcium scaling or black algae

    Welcome to the forum.

    The picture is too vague to be definitive but it doesn't look much like algae. That said, your test results (assuming they have been fairly stable) would not indicate algae, either, but would suggest scaling.

    What is the CH of your fill water? Has your pH drifted up higher than that from time to time?

    Slightly off the subject, but those results say you are not shocking your pool which would require an FC up around 12ppm or so with a CYA of 25ppm.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3

    Re: Calcium scaling or black algae

    The pH always seems to be drifting higher. This measurement was a few days after pouring a gallon of acid in and bringing the pH down to 6.8.

    I just measured the calcium of the fill. I took the water straight out of a spigot near the pool, because I didn't know how access it directly. I assume these are the same as long as they don't go into the water softener.

    I measured the CH of the water to be 420. Again, wow! I am in Southern Cal, and I know the water is hard, so I must be seeing the result of it.

    So, will I need to drain the pool to bring the CH down? What do I do about the high levels in the fill?
    20k gal., Pebble-tec, SWG, 60 gal pentair DE

  4. Back To Top    #4
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Calcium scaling or black algae

    Reverse osmosis is the only option to remove the CH. Best case with replacing water would get you near 500ppm. There are others on the board that are successful at maintaining their pools with 4 digit CH. You have to be VERY careful to keep your pH in check.

    Posted with Tapatalk ... sorry if I sound short ... hate typing on phone
    Jason, TFP Moderator
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  5. Back To Top    #5
    Melt In The Sun's Avatar
    Join Date
    Oct 2009
    Tucson, AZ

    Re: Calcium scaling or black algae

    It might not be algae or scale, just some variability in the surface of the pool. Can you get a close look with goggles? Black algae is little fuzzy bumps that obviously protrude out from the surface. You can scrape them with your fingernail and they're green.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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