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Thread: Could the black stuff be algae even though CC is 0 and water is clear?

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    Could the black stuff be algae even though CC is 0 and water is clear?

    Hello,
    We have something black on the bottom of the pool that has been getting worse, spreading to almost the whole bottom of the pool, but the pool water is clear looking. We have been using the TFP method of balancing the pool water and have had great success until now. We tried to scratch off a bit of the black stuff from the pool plaster surface in order smear it on a piece of paper to see what color it was but no matter how hard we scratched it, nothing came off on our fingernails and our fingernails broke yet not a thing came off. We also tried brushing it aggressively and not a bit came off on the brush or off the plaster. Also our CC has been between 0 and 0.2 at the very highest. The water looks clear, the black stuff is only on the plaster surface of the pool, not floating in the water as far as we can see.

    Could it be black algae if our CC is 0 and the water is clear? If it's not algae, what could it be? Our pool is one year and one month old. We do get a lot of leaf drop from neighbor's tree but we clean out the skimmers daily (they are full daily). We also clean out the inline leaf trap every weekend. And we've been cleaning the filters about twice a month even though it is a large cartridge filter and doesn't need to be cleaned that often. We use the FAS/DPD Chlorine Test in the Taylor K-2006 test kit. The kit is less than a year old and none of the chemicals have expired.

    I know our CYA is way too low, but we had high calcium (700) and high salt (4000) so we were going to drain some water and get those to the right level first before adding more CYA. Then we noticed the black stuff on the bottom of the pool and we were going to slam the pool first, but then we realized that the pH and TA were a little low (pH 7.0, TA 40) which was odd as our pH and TA tend to run on the high side. So we added some soda ash (per pool math recommended amount) and drained some pool water (about 15"). The salt is now 2800 (will need to add salt) but the CH was still very high so I brought some water to our pool supply place to see what they said the CH was and they said it was only 380. I checked our CH chemicals in our Taylor test kit and they have not expired and the kit is only about 10 months old. I refilled the R-0010 and the R-0011 anyway. But not the R-0012 as the store did not have it in stock. We keep the test kit indoors. I read some more about CH testing and tried various things to make the test more accurate but it is still about 650-700 according to our test. I generally don't trust pool store testing but they are using the same test kit as we are. The CH test also has lots of little purple specks floating in it which makes me think there is stuff floating in the pool but we just can't see it.

    Anyway, CH aside, the soda ash brought the pH up to 7.8 and the TA from 40 to 50. The pH is plenty high now but the TA is still a little low (we want it 60-80) so we bought some baking soda but have not added yet because the black stuff spread so much we decided to slam the pool ASAP. The pool store also said our phosphates are high at 200 which we usually ignore as we follow TFP and our pool is always crystal clear and CC has always been 0 or close to it, but maybe now we shouldn't ignore the phosphate level. The pool store also got a 0 reading for CC.

    I know that because our CYA is so low that we have probably not had the correct amount of FC in the pool at all times of the day especially since we only run the SWG at night and because our pool water is so warm and we are in Arizona so the pool gets a ton of sun and we have so much leaf drop. But, if it is black algae, why is the CC so low and why are we not able to scrap the black stuff off at all. I know black algae has a hard waxy/slime coat that requires a metal brush to break through the surface of the algae but wouldn't we be able to scrap some off with our fingernails? Could it not be algae but instead be the plaster is going defective? I know some people have posted about getting black mottling on their plaster quartz finish but if that is what we have why would it not come until over a year after the pool was built and why would it be spreading so rapidly? We do not have grass and have not used any fertilizers so it's not iron.

    We did run out and buy bleach today and dumped it in tonight (per pool math amount) but then I read the slamming instructions and realized I need to do this not so late at night when I have more time and I need to buy a lot more bleach as it is more involved then I realized. And we also need to buy a metal stainless steel wire brush since it might be black algae. But then again how can I follow the slamming steps on TFP if our CC is 0? Should I still go ahead and add the baking soda to bring up the TA or wait until after I slam the pool? Any suggestions on how to find our true calcium hardness levels? Should we go ahead and try slamming the pool and if so how do we know when to stop as the CC is 0? Should we add a little CYA now or just go ahead and wait until after we slam the pool?

    I know that this is like 10 different posts/questions but as it is all happening at once and I don't know what is pertinent since I don't know what it is or what is causing it, I included it all in one post.

    THANKS!!

    Levels today (7:00 pm) before adding bleach to slam with our Taylor test kit:
    pH 7.8
    FC 2
    CC 0.2 (somewhere between 0-0.2) (Pool store says CC is 0)
    TA 50
    CH 600 (my test says 600, pool supply place says 380)
    CYA 10
    Pool temp: 93 degrees
    Pool Store says Phosphates are 200
    Salt 2800
    It's a SWG pool with plaster quartz finish (QuartzScape super blue by NPT), cartridge filter, acid injector. We use the Taylor K-2006 with the FAS/DPD Chlorine test and AquaChek strips for salt.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    I get black marks from the wheels on my Polaris.
    In ground, 14,000 gallon, white plaster, unheated, stone waterfall, DE Filter, Rainbow 320 Cl, Polaris 3900, FloVis flow meter, F100 test kit, Circupool RJ30+ SWG, Circupool VJ1/Speck Badu EcoM3V variable speed pump.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Quote Originally Posted by Millty View Post
    Hello,
    We have something black on the bottom of the pool that has been getting worse, spreading to almost the whole bottom of the pool, but the pool water is clear looking. We have been using the TFP method of balancing the pool water and have had great success until now. We tried to scratch off a bit of the black stuff from the pool plaster surface in order smear it on a piece of paper to see what color it was but no matter how hard we scratched it, nothing came off on our fingernails and our fingernails broke yet not a thing came off. We also tried brushing it aggressively and not a bit came off on the brush or off the plaster. Also our CC has been between 0 and 0.2 at the very highest. The water looks clear, the black stuff is only on the plaster surface of the pool, not floating in the water as far as we can see.

    Could it be black algae if our CC is 0 and the water is clear? If it's not algae, what could it be? Our pool is one year and one month old. We do get a lot of leaf drop from neighbor's tree but we clean out the skimmers daily (they are full daily). We also clean out the inline leaf trap every weekend. And we've been cleaning the filters about twice a month even though it is a large cartridge filter and doesn't need to be cleaned that often. We use the FAS/DPD Chlorine Test in the Taylor K-2006 test kit. The kit is less than a year old and none of the chemicals have expired.

    I know our CYA is way too low, but we had high calcium (700) and high salt (4000) so we were going to drain some water and get those to the right level first before adding more CYA. Then we noticed the black stuff on the bottom of the pool and we were going to slam the pool first, but then we realized that the pH and TA were a little low (pH 7.0, TA 40) which was odd as our pH and TA tend to run on the high side. So we added some soda ash (per pool math recommended amount) and drained some pool water (about 15"). The salt is now 2800 (will need to add salt) but the CH was still very high so I brought some water to our pool supply place to see what they said the CH was and they said it was only 380. I checked our CH chemicals in our Taylor test kit and they have not expired and the kit is only about 10 months old. I refilled the R-0010 and the R-0011 anyway. But not the R-0012 as the store did not have it in stock. We keep the test kit indoors. I read some more about CH testing and tried various things to make the test more accurate but it is still about 650-700 according to our test. I generally don't trust pool store testing but they are using the same test kit as we are. The CH test also has lots of little purple specks floating in it which makes me think there is stuff floating in the pool but we just can't see it.

    Anyway, CH aside, the soda ash brought the pH up to 7.8 and the TA from 40 to 50. The pH is plenty high now but the TA is still a little low (we want it 60-80) so we bought some baking soda but have not added yet because the black stuff spread so much we decided to slam the pool ASAP. The pool store also said our phosphates are high at 200 which we usually ignore as we follow TFP and our pool is always crystal clear and CC has always been 0 or close to it, but maybe now we shouldn't ignore the phosphate level. The pool store also got a 0 reading for CC.

    I know that because our CYA is so low that we have probably not had the correct amount of FC in the pool at all times of the day especially since we only run the SWG at night and because our pool water is so warm and we are in Arizona so the pool gets a ton of sun and we have so much leaf drop. But, if it is black algae, why is the CC so low and why are we not able to scrap the black stuff off at all. I know black algae has a hard waxy/slime coat that requires a metal brush to break through the surface of the algae but wouldn't we be able to scrap some off with our fingernails? Could it not be algae but instead be the plaster is going defective? I know some people have posted about getting black mottling on their plaster quartz finish but if that is what we have why would it not come until over a year after the pool was built and why would it be spreading so rapidly? We do not have grass and have not used any fertilizers so it's not iron.

    We did run out and buy bleach today and dumped it in tonight (per pool math amount) but then I read the slamming instructions and realized I need to do this not so late at night when I have more time and I need to buy a lot more bleach as it is more involved then I realized. And we also need to buy a metal stainless steel wire brush since it might be black algae. But then again how can I follow the slamming steps on TFP if our CC is 0? Should I still go ahead and add the baking soda to bring up the TA or wait until after I slam the pool? Any suggestions on how to find our true calcium hardness levels? Should we go ahead and try slamming the pool and if so how do we know when to stop as the CC is 0? Should we add a little CYA now or just go ahead and wait until after we slam the pool?

    I know that this is like 10 different posts/questions but as it is all happening at once and I don't know what is pertinent since I don't know what it is or what is causing it, I included it all in one post.

    THANKS!!

    Levels today (7:00 pm) before adding bleach to slam with our Taylor test kit:
    pH 7.8
    FC 2
    CC 0.2 (somewhere between 0-0.2) (Pool store says CC is 0)
    TA 50
    CH 600 (my test says 600, pool supply place says 380)
    CYA 10
    Pool temp: 93 degrees
    Pool Store says Phosphates are 200
    Salt 2800
    It's a SWG pool with plaster quartz finish (QuartzScape super blue by NPT), cartridge filter, acid injector. We use the Taylor K-2006 with the FAS/DPD Chlorine test and AquaChek strips for salt.
    Can you post some pictures of this 'black stuff'?

    Dom
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    IMG_9207-2.jpg

    - - - Updated - - -

    IMG_9207.jpg

    - - - Updated - - -

    It's really hard to get a picture of it because of the reflection of the trees and clouds and there is a breeze so there are ripples across the top of the pool. It looks worse than the picture shows. Normally it would be all one color blue and wouldn't have the dark black at all.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    This looks to possibly be metal staining....that's how it looked in my pool.

    Try crushing vitamin c tablets, put them in a nylon and lay over a spot of that.

    if it disappears it's metals. Ever use copper algecide?
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    IMG_5584.jpg

    - - - Updated - - -

    IMG_4074.jpg

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Thanks for the info, I didn't think it could possibly be copper because we've never used any algaecide at all. And we don't fertilize our yard. The only chemicals or additives that we have ever put into the pool are CYA, salt, bleach, soda ash, and muriatic acid, plus the chlorine the SWG generates. The start up guy used some sort of CalHypo or Dichlor or something but we quickly corrected his screw up and we also had the water tested for metals last year and there wasn't any copper or other metals, but that was the pool store so don't know how accurate it was. Maybe our neighbor used something like a fertilizer and it blew over the fence but that would be weird because the entire bottom of our pool is turning black so don't know how that much could blow over. Anyway, I'll run out and buy vitamin C and try it and let you know.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    How do you clean off the marks made by your Polaris pool cleaner? Oh, I just realized it can't be caused by the wheels of our pool cleaner because the black stuff is on the stairs and sides of stairs and the pool cleaner doesn't go there. But thanks.

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    Mod Squad pooldv's Avatar
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Water looks good! You can try rubbing a trichlor puck or some dichlor in a sock in a different spot for 5 to 15 minutes to see if it lightens the stain. If it does then it is organic. Yes, it is possible to have black algae and 0 CCs. But, it seems unlikely that black algae would be so wide spread so fast.
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    We bought vitamin C and rubbed it on some spots, didn't do anything but did turn the plaster yellow, don't know why, hope it comes off. We also bought a trichlor puck and it didn't remove the black, not sure we rubbed long enough, will try again tomorrow.
    25'x37' L shaped: 4' play pool and 8.5' deep end, w/7x11 spa, 26k gallon, gunite w/plaster quartz, travertine coping, IntellifoVS x2, C&C Plus 520 cart filter, inline leaf trap, IC40 swcg, IntelliPH, IntelliTouch auto w/screen logic, MstrTmp 400k heat pump, 2 Intellibrite LEDs & 1 globrite, 3 sheers, 3 baja bubblers, 1 telescoping spa bubbler, 2 Venturi skimmers, TK-2600 kit. Built 2015.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Is it a dark black, or more of a grayish color? From the pics it almost looks like scaling. I'm no expert, though. Have you put all of your readings in PoolMath and checked your CSI?
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    Mod Squad zea3's Avatar
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Why high CH and high pH I am pretty certain you have calcium scale and not black algae. I know your area has very hard water, so check the calcium level of the water you use to top off the pool. The best course of action would be to dissolve as much of the calcium scale as you can, then drain and refill the pool with lower CH fill water.

    you need to lower the TA to 70ppm and the pH to 7.2 and keep them there so the calcium will release from the surface of the pool. Brush the pool daily and clean your filter when you see a 20% rise in pressure. As the calcium releases you will be needing to clean the filter more frequently.

    You can search "calcium scale removal" in the search box for more information.
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    Mod Squad pooldv's Avatar
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Aha! Maybe it is scale. Put some dry acid in a sock and rub it on a spot to see if it dissolves it.
    There are several options for removing scale.
    The least invasive is to lower your CSI to -0.8 to -0.9 and brush as often as you can stand to. This is a fairly slow process, about as one as it took for the scale to form. You can use a stainless steel brush for more aggressive brushing.
    The next least invasive is an acid bath, The Zero Alkalinity Acid Treatment, this will shorten the plaster life a bit
    the most aggressive is to drain and acid wash the pool. This will remove plaster and shorten it's life.

    To prevent scale from occurring maintain your CSI between -0.3 and 0. PoolMath will calculate it, tweak PH and TA to change the number.

    More here, Pool School - Calcium Scaling
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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Could it be scale because when we noticed the black stuff, (it looks grey in photos), our pH was 7.0 (actually 6.8 based on the base demand test), the TA was 10, and the CSI was -1.44 (The levels at the bottom of my first post were a couple days after the black stuff formed and after we had added stuff to bring up pH and TA) After adding soda ash and baking soda, the pH is now 7.8 and the TA is 60. The CH was 380 according to the pool store (I watched him titrate it and he did it correctly using the Taylor Kit). My test showed the CH was 600 but I think there is something wrong with my test chemicals. When I do the CH test, there are a ton of floating red specs that stay red, the water turns blue but it's hard to tell because the specs stay red, if that makes any sense. The blue drops (R-0012) for the CH test are really thick and hard to squeeze out of the bottle, so I need to get some new R-0012. I think we put the stronger acid in the injector and didn't adjust the % to account for stronger acid. I'm going to adjust the acid injector up a little to get the pH to 7.6.

    Where do I get dry acid to test if it is scale? What kind of acid is dry acid? I think I'll bring the water to another pool store and see what they say the calcium is.

    Our water hardness is 250-350 which includes calcium, magnesium and a couple other minerals. So I guess that is pretty hard. Their report doesn't break out calcium but I might call the city to see if they'll tell me the calcium level. I'd test it myself but since my kit is screwy, hey, maybe that would be a good test to see if my test chemicals really are screwy. Going to try that.

    Do you think it is safe to swim in the pool? The FC is 3 and the CC is 0.

    One thing i did notice is that the black stuff is only on the bottom of the pool and low down on the sides, but the baja shelf is perfectly clear. Our baja shelf is really shallow, like 5". The top two stairs are clear too. Weird, eh?

    Thanks for all the great help! I love a mystery but hate not being able to use the pool.
    25'x37' L shaped: 4' play pool and 8.5' deep end, w/7x11 spa, 26k gallon, gunite w/plaster quartz, travertine coping, IntellifoVS x2, C&C Plus 520 cart filter, inline leaf trap, IC40 swcg, IntelliPH, IntelliTouch auto w/screen logic, MstrTmp 400k heat pump, 2 Intellibrite LEDs & 1 globrite, 3 sheers, 3 baja bubblers, 1 telescoping spa bubbler, 2 Venturi skimmers, TK-2600 kit. Built 2015.

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    Re: Could the black stuff be algae even though CC is 0 and water is clear?

    Hey, how did you remove the black marks on your pool surface caused by your Polaris wheels? Did yours look like our pictures? We've brushed and brushed and can't get it off. A pumice stone worked but probably sanded off a layer of plaster too. We just noticed some black stuff come off onto our hands from the black rubber on our cleaner's wheels--it's like its disintegrating. No surprise as rubber doesn't last in Arizona. And I noticed the black stuff isn't on the top steps or the Baja shelf where cleaner doesn't go. It's on the other steps but we set it on those steps sometimes.
    25'x37' L shaped: 4' play pool and 8.5' deep end, w/7x11 spa, 26k gallon, gunite w/plaster quartz, travertine coping, IntellifoVS x2, C&C Plus 520 cart filter, inline leaf trap, IC40 swcg, IntelliPH, IntelliTouch auto w/screen logic, MstrTmp 400k heat pump, 2 Intellibrite LEDs & 1 globrite, 3 sheers, 3 baja bubblers, 1 telescoping spa bubbler, 2 Venturi skimmers, TK-2600 kit. Built 2015.

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