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Thread: Black Algae or Plaster/Gunite problem

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    Black Algae or Plaster/Gunite problem

    Last year I had one patch, this year it has spread. I am convinced that this stain is coming through the plaster, perhaps with algae attaching itself to it. Could it be the gunite? any ideas, thoughts? shocking doesn't seem to budge it and it doesn't brush off. It is very rough to the touch.
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    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    BoDarville's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    Gently scrape a sample of the suspected black algae with your fingernail and then smudge it on plain white paper. If the smudge scrapes off and is a greenish color, then it’s very likely black algae.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
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    Re: Black Algae or Plaster/Gunite problem

    Thanks for the response. I tried scraping and it seems like bits of pieces of plaster coming off. The more I brushed the stain the lighter it got but then a brown brick color started showing through. I do have algae at the moment and I think some green algae was living on top of the stain, but I hate to say that I still think it looks like its coming through the plaster and on the floor. Who would I call out to give me a diagnosis? It looks like it needs replastering to get rid of it. I don't really think its a stain, I think its black/brown rebar or something coming through.
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Re: Black Algae or Plaster/Gunite problem

    Not really sure quite yet.....it is not rebar, i am sure of that.

    Of course, the first step to identifying the stain is to post a current set of test results. Can you do that?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Black Algae or Plaster/Gunite problem

    Thanks Duraleiigh. yes, I'll post them shortly. I just bought one tab from the shop to see if it makes a difference when I try and scratch over other spots on the ground.
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Re: Black Algae or Plaster/Gunite problem

    Here are my readings:

    CH 15
    Combined CH 0.5
    PH 7.2
    AK 60
    CYA Still able to see the dot. Added granular this morning.
    CH No regent to test

    It seems the black dots are all around the pool, mainly on the floor. I tried with a tab to rub over the dots but nothing happened. I definitely have algae in places but this black stuff looks like dirt that won't wipe off.

    How do I upload more photos? I tried taking better ones for you to see.
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Texas Splash's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    Your FC is high for not having any stabilizer recorded yet. In fact, because your FC is high (over 10), and your pH is showing low (usually it goes up when FC is elevated), I would recommend allowing your FC to drop just under 10 then re-test your pH to make sure 7.2 is a true/accurate reading. Once you validate the pH at 7.2, then increase FC to "12" (assuming your CYA goes to 30). If your CYA goes higher than 30, then your FC may need to go higher as well.

    We really need a CH reading. That's important to analyze your plaster and "CSI" level. You should be able to get some CH reagent locally. If not, I would request a refill from TFTestKits.com as soon as possible. By looking at your thread here, we want to know if we can rule-out a plaster problem as opposed to simply treating an algae problem.

    For photos, have you tried linking your photos from Photobucket? That's what many of us do here on TFP. Upload your pics to Photobucket (free), then copy & paste the IMG code for that pic from Photobucket to your TFP post. Works great.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    Re: Black Algae or Plaster/Gunite problem

    Catherineb:

    A few points of clarification on your test results...Assuming the first CH result listed is the free chlorine reading. If so, just want to confirm that it really is 15 ppm or if a decimal is missing and you intended to say that it is 1.5 ppm. If it really is 15, then that is too high - even for shock (SLAM) levels - for your CYA which is close to zero given that you can see the dot.

    I would also try to get a calcium (CH) test result as this may be contributing to the problem you are experiencing. Plaster pools need some calcium present to guard against plaster damage.

    Also, your pH may be lower than 7.2 if the chlorine level is indeed 15 and pH was tested at that chlorine level. High chlorine levels (above 10 ppm) can skew the pH results. If so, I would retest pH when the chlorine level drops below 10 ppm.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
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    Re: Black Algae or Plaster/Gunite problem

    I recently lowered my PH and then started to shock but then my CH had disappeared in a matter of hours so I tested my CYA only to find out I had none. I also tested my CH with the 0.5ml with one drop of 0871. Perhaps my reading is off.

    I will order some regent from TFT to test my CH.

    How long before I get a reading on my CYA? Should I add some more. I know it can take a week to get a proper reading?

    I'll try the photobucket and upload a few more pics.

    Should I do a slam to see if it makes a difference?
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Re: Black Algae or Plaster/Gunite problem

    Although it may take about a week for newly-added CYA to appear in test results, after 24 hours I would dose chlorine according to the new target CYA level. In other words, you can assume that the CYA you added is present in the pool after 24 hours for chlorine dosing purposes. I would keep the pump running until the granules dissolve. BTW, what CYA level were you targeting when you added the granules?

    Quote Originally Posted by Catherineb
    Should I do a slam to see if it makes a difference?
    We need to get at the root of what is causing the problem with your plaster, so I would hold off on the SLAM until we have a proper diagnosis.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

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    Re: Black Algae or Plaster/Gunite problem

    I just retested and got the same results for my chorline and cya. My PH I would say yes it could be lower than 7.2 Looks more like 7.0. I lowered it this morning, it hasn't always been that low. My PH is always running on the high side.

    I'll see what it is tomorrow. Meanwhile I'll order the test for the calcium. Last year I drained the pool as the calcium was way too high. I doubt it's too high but will get the reading.

    Thanks. Meanwhile I am still trying to figure out the photobucket and will post additional photos.

    - - - Updated - - -

    I was aiming for 30 for my cya maybe 40.

    So, tomorrow when the sun comes out, my chlorine will disappear. Should I just keep my Chlorine to the correct level at about 6 or 7?
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Re: Black Algae or Plaster/Gunite problem

    berrellsc's Library | Photobucket

    Can you see my pics?
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    BoDarville's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    Yes, I can see your pics. After looking at the pics, it does look like black algae, but given that the smudge test you did earlier today was inconclusive, I'm not yet ready to definitively say it's black algae. BTW, there are some black algae pics in this article that you may want to cross-reference with yours: Black Algae.

    It is possible that you may have both worn plaster and black algae. Black algae most often afflicts porous surfaces like plaster. If your pool's plaster is cracking and flaking, it results in even more spots where black algae can set up shop. Do you know how old the plaster is?

    Another thing you can try (and it is crucial for treating black algae anyway) is brushing the black spots with a stainless steel brush. Plaster that is in good shape should not flake off when brushing.

    We'll see if anyone else weighs in on what they see in your pics. For now, I would keep chlorine in the range of 6-8 ppm, basically at the high end of the recommended range for your CYA plus 1-2 ppm.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

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    Mod Squad pooldv's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    If you click the pic in PB, copy the IMG code to the right of the pic and paste it in your post it will show up in the thread like this
    TFP Moderator
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    Re: Black Algae or Plaster/Gunite problem

    Thank you Pooldv for the helpful info on posting my pics.
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Re: Black Algae or Plaster/Gunite problem

    Thanks BoDarville.

    I triedc yesterday and today to check out the photos on the site but they won't open. I can see 3 boxes only that don't open.

    My plaster in 11 years old. I think it started with me trying to brush with the steel brush on a patch that seemed to get worse in appearance the more I brushed it. I think you are right, there are like little pours all around the pool with a black algae dot in them. How on earth will I get rid of it. I've read and hard it is to get rid of.

    When I try brushing the floor with a steel brush, I see no difference. I don't think I have the muscle power. When I do it on the wall, I see powder coming off and it seems to lighten in color (I think algae was on top of it).

    I just tested again and my Chlorine is 6 but the PH is still 7.0. Should I increase the PH a little?

    There are 2 0871 reagents on the TFT page, are they the same except one is slightly bigger?
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

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    Mod Squad pooldv's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    Yes, raise PH to 7.5ish. Keep PH between 7.2 and 7.8. Yes, the R-0871s are the same.
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    BoDarville's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    Catherineb:

    Not sure why you are not seeing the pics in the Black Algae article. In any event, I am seeing some similarities between the pics in the article and the pics you uploaded to Photobucket. Based on the evidence presented so far, I'm inclined to believe that you have both black algae and a worn plaster issue. If there is a way for you to do the smudge test I mentioned earlier in this thread using a sample from a more stable section of plaster, it would help build the case for or against black algae. As for the plaster, this may be one of those things where a second opinion from a trusted pool maintenance company may be beneficial since there are certain things that are difficult to conclusively diagnose over the internet.

    The thing with black algae is that shocking (or as we call it, SLAMming) alone will not budge black algae. Unlike green or mustard algae, black algae requires maintaining an elevated chlorine level somewhere between the high end of the normal maintenance range for your CYA, but short of SLAM levels. It does, however, take more time and will necessitate much more “elbow-grease” on your part. Brushing several times a day with a stainless steel brush is the most critical aspect of removing black algae. Proper and regular brushing will rupture black algae’s protective barrier and prevent it from reforming. Removing this protective coating will allow the chlorine to attack the algae itself.

    But if it is time for a replaster, they should remove much of it as part of the prep and make sure that all black algae has been removed prior to installing the new plaster.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  19. Back To Top    #19

    Re: Black Algae or Plaster/Gunite problem

    Thanks BoDarville. I didn't see your response until now as I have been waiting for my new regeants to arrive to test the CH. It reads 180. I am going to do the test again as that seems low. It should be at least 250, correct?

    So, what if I drained the pool to powerwash the black algae, would that work? I think I have both too. Definitely worn plaster, but only in a few patches where the brown is showing through. I wonder could the patches be done or does the whole pool need to be replastered?

    I guess I will need to call out a pool company to confirm. Not Leslies, but you mean a pool company like to call out?

    I'm going to Vegas this weekend. Perhaps I'll win a few $$$$ to get a replaster job done.

    Also with this bad plaster is it causing anything else to enter the pool?

    Thanks
    Cathy
    10,000K plaster, cartridge filter Pentair 420, no heater, in ground pool, Pentair Pump. Taylor K-2006 kit.
    Dallas, TX

  20. Back To Top    #20
    Mod Squad pooldv's Avatar
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    Re: Black Algae or Plaster/Gunite problem

    I would be nervous about draining and pressure washing, it could blast so e more plaster off the the pool.

    Bad spots can be patched. But, you should have the plaster company (or two) evaluate the rest of the plaster to see if that is worthwhile.

    Yes, CH needs to be 250 ppm.

    I would focus more on brushing and elevated FC levels or winning some cash!
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