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Thread: Is this a sign of trouble?

  1. Back To Top    #1

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    Is this a sign of trouble?

    I've noticed small black spots forming on the walls of my pool. Brushing doesn't seem to affect them. Scraping with a fingernail breakes them up some but them seem to be embedded into the plaster some. Any thoughts what they might be?

    The water has been clear and the chlorine has been maintained for several weeks now.

    FC 10 (CYA ~80 LAST CHECK)
    CC 0
    pH 7.6
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

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    Butterfly's Avatar
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    Re: Is this a sign of trouble?

    Possibly black algae. BA are usually round, black spots. If you remove one and smear it on a white paper, it would appear green (if it is black algae). I think waste/Ted said to smear it on the back of a white business card.

    What are your other test results?

    Also, has the pool been let go for a while, allowing FC to drop?

    Do you have pics?
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  3. Back To Top    #3

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    Re: Is this a sign of trouble?

    I haven't tested everything lately but last I checked ~early May

    CYA 80
    CH 410
    TA 190
    TEMP 88 F

    I have added water 4 or 5 times since opening, usually an inch at a time. The pH has gone up aas high as 8 about 2 weeks ago and I added MA to lower. I have also added MA twice and aerated to try and lower TA. The CC has been steady at 0 with one test o month or so back showing a trace. Other than that the FC has dipped low (4) a couple of times since opening, last one 3 weeks ago.
    Thanks.
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  4. Back To Top    #4

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    Re: Is this a sign of trouble?

    You may need to start the shocking and brushing process for black algae. It is tenacious but can be eradicated.

    Having a good test kit will help you immensely. You need to be able to accurately test for FC, CC, CYA, TA, pH, and CH. Foolow the link in my sig line to get a TF-100 test kit if you haven't ordered one already.

  5. Back To Top    #5

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    Re: Is this a sign of trouble?

    I have a Taylor kit. I rechecked all my numbers last night and they agreed with the previous post.

    How long do I need to shock for black algae? Is it the same basic process for "regular" algae?

    What does black algae look like? My spots are smooth and flat, pretty much even with the plaster surface. I found a pic online that showed globules sort of like a mushroom. I took some under water pics yesterday if the come out ok I'll post as soon as I can.
    Thanks.
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

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    JasonLion's Avatar
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    Re: Is this a sign of trouble?

    Getting rid of black algae is a project. Lets hope you don't actually have black algae. One good check for black algae is that it won't really all brush off and yet you can get some of it off. Also, if you scrape some off with a finger nail and smear that on a piece of paper it will look green, while on the pool it tends to look black.

    If it is black algae, you can try rubbing it off with a trichlor tablet.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  7. Back To Top    #7

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    Re: Is this a sign of trouble?

    Here are some pictures of the spots. Hopefully they are clear enough. I brushed with a stainless steel brush without much effect. I also tried to get a piece to put on white paper to see if it was green but no luck. Most of the spots are too small to get hold of. A couple of them were big enough to break open and it did seem to be green behing with fine hairy looking roots. So, what's the verdict? Black algae or not?

    Thanks.
    Attached Images Attached Images
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  8. Back To Top    #8

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    Re: Is this a sign of trouble?

    more pics...
    Attached Images Attached Images
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  9. Back To Top    #9

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    Re: Is this a sign of trouble?

    one more
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  10. Back To Top    #10

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    Re: Is this a sign of trouble?

    one more
    Attached Images Attached Images
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  11. Back To Top    #11
    Richard320's Avatar
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    Re: Is this a sign of trouble?

    Looks like black algae to my unprofessional eye. 302 and 301 also look like some caalcium scale, for what it's worth.

    Off to the pool store with you - time to buy an algae brush! It fits in your pole like a normal attachment, but it's a small -maybe 6" wide, coarse, stainless steel brush.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  12. Back To Top    #12

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    Re: Is this a sign of trouble?


    I got the stainless brush today and brushed once so far. It didn't seem to faze it much but I'll keep trying. I'm going to raise my base FC level until this is cleared. Do I need to shock for this? My cc levels have been 0 for at least a couple of weeks.
    Thanks for the input on the calcium scale, I didn't know I had that too. Not surprised though since my CH has been high since I acquired the pool. How do you fix that problem?
    Does lowering the pH help to fight the BA?
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  13. Back To Top    #13
    Richard320's Avatar
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    Re: Is this a sign of trouble?

    The search function is your friend.

    Type in "black algae" just like that, with the quotation marks. You'll get a lot of hits. Look for the threads with lots of replies.

    I'm no expert, especially not with this problem.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  14. Back To Top    #14
    JasonLion's Avatar
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    Re: Is this a sign of trouble?

    Lowering PH helps prevent calcium scaling, but won't have any effect on black algae.

    I have a suggestion. Try rubbing one of the spots with a trichlor tablet for a minute, and holding a vitamin C tablet against another one for 30 seconds, and see if either one changes in appearance.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  15. Back To Top    #15

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    Re: Is this a sign of trouble?

    I tried the vitamin c and trichlor tab experiment over the weekend. I did not see any change with the trichlor tab. The spot did fade with the vitamin c. I'm going to do it again since it was tough to do given the spots are mostly 4-5 feet down and are still fairly small.

    So what does that mean?
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

  16. Back To Top    #16
    Mod Squad Bama Rambler's Avatar
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    Re: Is this a sign of trouble?

    If the vitamin C affected it then it means it's most likely iron stains. If there are a bunch of them you may consider an AA treatment but if there's only a few the tablet is a better way to go.
    Dave J. TFP Moderator
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