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Thread: Black spots on bottom of pool??

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    Unhappy Black spots on bottom of pool??

    My gunite pool is about 18 years oil. Last summer I started getting a few small black spots on the bottom of the pool. This summer I have many more, no matter how hard I brush I cannot get rid of them. Algae treatments do not seem to help. My husband used to do all the pool work, however since he passed 3 years ago I have tried to learn it all as I cannot afford a pool service. This looks terrible and is so frustrating! I can take care of it if I know what is wrong. I am wondering if it is the gunite wearing off? Or maybe the algae is very bad and stubborn and I am not strong enuf to brush it off. Any help?? I am in Texas and I know as it keeps getting hot I will have even more problems. Recent pool water tests show I am doing ok except the phospates were up, which I am working on, and the cyanic acid was about 100.

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    Default Re: Black spots on bottom of pool??

    Regardless of what your black spots are, with CYA => 100+ ppm, you *must* (a) read the "Best Guess Chlorine" page and (b) get a K2006 test kit. You can not keep a pool algae free at the chlorine levels possible with a conventional test kit. Links for the Best Guess page, and for the K2006 on Amazon are in my signature.

    But, to firmly determine what the spots are, swim down, and scrap the spot with your fingernail. If the spot IS black algae, you'll end up with a bit under your fingernail. Swim up, and smear the algae on a bit of white cardboard or the unlined side of an index card. Black algae will look almost black, but will smear dark green.

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    rkrgk is offline --General User-- Thread Analyst rkrgk 0
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    Default Re: Black spots on bottom of pool??

    It seems as though you have somewhat similar situation to mine. I have a hard time removing the black spots as well. It was much worse a month ago, and just like you, I used to think my gunite surface is wearing off, and just let the algae grow slowly on the walls, finally when I realized, I got a stainless steel wirebrush and started scrubbing off daily. I got it to a point where it doesnt go off anymore, though there are still some spots. You could read my post here, http://www.poolforum.com/pf2/showthr...otty-and-dirty
    I still havent found any real easy solution to knock the black algae off the walls, and scrubbing doesnt remove all of them, so I am still working on them, you can see pictures there as well. Keeping high FC doesnt seem to make it easier to remove them since they seem to have a much stronger root on the walls and chlorine doesnt seem to affect the inner side of the algae colonies. Probably you could learn something from my experience and we could share some info which will help me as well. I am at Phoenix.
    18x32 kidney 15K gal IG Gunite pool; skimmer tabs; Hayward DE6000 DE filter; Hayward/AO Smith Superflow 1 speed pump; 12 hrs; heat pump, fountain or waterfall; Taylor K2006C ; utility water; summer: none; winter: none; android tablet; PF:8

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    Default Re: Black spots on bottom of pool??

    Quote Originally Posted by rkrgk View Post
    Keeping high FC doesn't seem to make it easier to remove them since they seem to have a much stronger root on the walls and chlorine doesn't seem to affect the inner side of the algae colonies.
    High chlorine, held consistently over a period of weeks, is effective, but will NOT eradicate algae that has penetrated into cracks where chlorine can't reach.

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    rkrgk is offline --General User-- Thread Analyst rkrgk 0
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    Default Re: Black spots on bottom of pool??

    PoolDoc, I read somewhere that sprinking trichlor granules/cal hypo directly on top of the black spots or scrubbing the black areas with trichlor pucks with a holder (while keeping a lower pH 7.0) might help? And keep the pump switched off for the day or so for the granules to work directly on the spots and srcubbing. Do you think it will help?
    18x32 kidney 15K gal IG Gunite pool; skimmer tabs; Hayward DE6000 DE filter; Hayward/AO Smith Superflow 1 speed pump; 12 hrs; heat pump, fountain or waterfall; Taylor K2006C ; utility water; summer: none; winter: none; android tablet; PF:8

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    Default Re: Black spots on bottom of pool??

    Pool Doc, thank you for your reply! I appreciate any help with this pool. I was waiting for payday but I am ordering that pool kit you suggested from Amazon, you are right in that I need to be testing for all this stuff myself instead of at Leslie's. I am hoping the booklet that comes with it will help me better understand the chemical interactions. I did take them another sample a few days ago and my cyanic is down to 80, which is better, and the phosphates are staying under 100. I am adding their PhosFree product weekly. I did treat last weekend with their black algae killer. I cannot see any diff tho. I am brushing twice a day, also with a small steel brush on the spots and they are maybe improving a bit. Hard to tell, there are hundreds of spots and there is not enough strength in my arms or time in the day to budge them! Most are in the deep end. I guess I am going to have to live with an ugly pool bottom. I cannot keep the FC at high levels for weeks, I have dogs that swim in and drink the water and keeping them safely away from the pool for more than a few days is very hard. The water is very clear and nice to swim in, the walls of the pool are good, spots are all on the bottom. I did scrape it with a toe tho and it smeared green.

    I would love to see other people's pics of their spots but I cannot seem to open any, it says I don't have permission??

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    Default Re: Black spots on bottom of pool??

    What post are you using, that has pictures you can't see? (URL?).

    High chlorine is not a risk for your dogs; until a few years ago, there was NO upper limit on the chlorine in drinking water! I'd be more concerned about CYA, and some of the additives you are using. It's not that I know they are bad for dogs; it's just that I don't know what effect they have.

    Be careful about the Taylor booklet; it has some bad advice in it. The kit is excellent but the booklet mostly promotes pool industry standard methods and doctrine -- NOT the BBB method.

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