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Thread: Black algae

  1. Back To Top    #1

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    Black algae

    I have a gray plaster pool and noted black spots in two areas of the pool. I have scrubbed bb daily and treated spots with "spot kill". In the morning there are occasional spots that reappear but as soon as the pump runs they disappear. I plan to continue bb daily for a week and then q week. I shock the pool weekly with 10% bleach ( I had high CYA levels and after draining 2/3 water they came down to 40). Water analysis pH 7.6, FC 3.5, TA 120, CYA 40 and has remained pretty stable for 2 weeks. I was told at store that I will never get rid of it and should empty, acid wash and start from scratch.
    A post somewhere else suggested treating it with approx 8 gallons of 10% bleach followed by two gallons of Ammonia Hydroxyde, but I am afraid of just adding stuff.
    It is a lot of work daily and I am afraid it will continue making my pool ownership more work than fun.
    Any advise??
    15000g Gunite
    48sqft DE Filter

  2. Back To Top    #2
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    Re: Black algae

    first thing is to determine if they are really black spot algae or something else. Black spot algae is slow to start and equally slow to get rid of. It occurs in pools that have been neglected for a period of months (having too high a CYA for months would qualify).
    First, are the spots round? if they are not it's not black algae.
    If they are try this:
    scrub a spot with a stainless steel algae brush (necessary to get rid of black algaie in a plaster pool!)
    Hold a trichlor tab on the spot for about 1 hour. (You can put it in an old cotton sock and hold it down with your pole or weight it down.)
    Scrub again... If is it black agale the spot should be ligher and smaller from the bruhing and high chlorine.
    The way to kill black algae is to raise the FC to about 40 ppm and HOLD IT THERE and brush several times a day until the algae is killed. Because it grows in layers and has a very resistant cell membrane you need to keep brushing with the stainless steel algae brush.

    Using the chlorine and ammonia is an old trick to create monochloramine but that is more effective against green and mustard algae and is, in fact, how some of the chlorine 'enhancers' works (like green to clean and yellow out)

    If the spots do not respond to the brushing and trichlor above then they are NOT black algae and we need to try some other tests to see what the stains are from.

  3. Back To Top    #3

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    Re: Black algae

    Thanks for the input. The spots are about 1 cm wide and round and fade with the brush/tablet trick. I can calculate how much liquid CL to get to 40 PPM but how do I Know how much to add daily to keep it there? Test kit goes up to 3-5 PPM. Is it a lost battle? Should at some point empty and acid/bleach wash the entire thing?
    15000g Gunite
    48sqft DE Filter

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    frustratedpoolmom's Avatar
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    Re: Black algae

    Hi there,

    You said two areas, how much spotting are we talking?

    This probably resulted from the high CYA, once present, BA is a BEAST!

    I would follow Waterbear's advice, raise the FC up - but I'm going to advise being more conservative, I think a FC of 40 is too high. With your CYA of 40 I think you can shock to 25, keep it there for 48 hours by testing and adding bleach, but the important part to destroy the BA shell is brush several times a day while the FC is that high. Use the Pool Calculator to determine how much bleach to hold the FC at 25.

    In order to test that high, you need the FAS-DPD test, you can buy the full TF100 kit or just the test to supplement your kit. What kit do you have now? If it's a K2005, then just supplement.

    It's not a lost cause. You just need to be diligent, especially about the brushing and bleach additions, as that what will do it.

    AFter the first 48 hours of high shock, you can let the FC drop to your normal "shock level" which is 16 according to the CYA Chart. Keep it there until you experience no overnight FC loss, and the algae stops growing back.

    Then, run your FC at slightly elevated FC levels between 6-10 ppm for about a month or so, and brush every day these areas. It's the frequent brushing that is key. Holding part of a trichlor on the stains, if there are any residual staining, can help fade them. Keeping your FC above the minimum level for your CYA is key to preventing the BA from returning. For your situation, I would never let the FC drop below 4 at any time.

    I wouldn't resort to draining them yet - but this is without seeing the spots. Any chance you could post a pic?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: Black algae

    Thanks. I will get the kit and do the calculations. Is it safe to swim with a FC of 6-10? We are talking one month of the summer... The two areas are on two corners on the floor about 4 x 4 feet each and there are about 50+ spots. Now, for the past two days they have not recurred but I only added two gallons of liquid shock (10% Cl) last night and the FC was 3.5 before that. Would if be enough brushing morning and night? For how long? I am afraid if I stop, they will recur.
    If they come back I will try to post pictures.
    Hope I can defeat this beast.
    15000g Gunite
    48sqft DE Filter

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    frustratedpoolmom's Avatar
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    Re: Black algae

    Perfectly safe. Any FC level below shock is safe to swim (above the minimum of course )

    The key is brushing, to destroy that outer shell so that the chlorine can attack the insides of the algae. If morning and nite is all you can do, it's all you can do. The more the better, especiall when you are holding it at shock level. If they are disappearing that is a good sign that you won't be left with residual staining. Keep brushing, even if you don't see them, just brush the general areas.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

  7. Back To Top    #7
    Guest

    Re: Black algae

    I still say nuke the pool to 40 ppm and brush, brush, brush.
    It will take care of the problem very quickly.

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    Re: Black algae

    Just took a water sample to the local Leslies. It is so unreliable. First, they do not give me anything over 5 on the FC. Now they say the CYA is 100 after last week it was 40. They measured Phosphates ??? and they are at 300. Of course sold me Phos free (39 dollars). everytime I go it seems you walk out with something new. Thanks god for your website. I ordered the F100 kit from the web site. I redid the calculations and I think if the CYA was truly 100 I would have needed 3 gallons of 10% liquid shock instead of the two gallons I added yesterday. Got back from work, had not brushed since yesterday evening and it looks beautiful. No spots whatsoever. I am making the transition to your BBB system and fighting BA. Never going back to local store. I will be leaving town for a week and was planning on adding two or three gallons of 10% shock and have a friend come once daily to brush. Hope I do not find a mess when I get back.
    As far as the high CYA I am just going to have to use more bleach since we are under water restriction in SA and cannot empty pool. Of course I would like to retest when I get my new F100.
    One last thing do I keep tablets in the chorinator. If so, what type. I know it will keep raising the CYA.
    Have a DE filter and I am running the pump 16 hours per day. Cleaned it one month ago. Pressure 18.
    15000g Gunite
    48sqft DE Filter

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    frustratedpoolmom's Avatar
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    Re: Black algae

    Remove the pucks tonight. Toss them. Stick to bleach till we know what your numbers REALLY are.

    Return the phos remover - you were pool stored.

    I'll be glad for you (when your test kit arrives) because you can't trust the pool store testing. And by doing your own testing, you aren't tempted or convinced to buy something you DON'T need (phos remover.)
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: Black algae

    I will return that stuff tomorrow.
    The kit may not arrive before I leave (Thursday) for one week. Any advise on what to put before I leave if I cant measure things accurately. Nobody will be using the pool for that week. If I get the kit I will post readings before I leave. Thanks a million. I am actually enjoying this challenge. Hope I can enjoy the pool again.
    15000g Gunite
    48sqft DE Filter

  11. Back To Top    #11
    frustratedpoolmom's Avatar
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    Re: Black algae

    You're leaving? Ugh. That does present problems.

    Anyone who can add bleach for you while you're gone?
    Can you keep the pump running/is it on a timer?
    Do you have a solar cover?

    Pick up a qt of Polyquat 60 algaecide. No other type will do.

    It should say "Poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylene dichloride 60%" as the Active Ingredient. (Say that five times fast to the sales clerk )

    You don't say how big your pool is - ** see below. Add 11 ounces per 10,000 gallons of pool water. Add it on Wednesday morning and Keep the pump running. Wednesday Night, Shock the pool back up to 25 (assuming your CYA is 40). Cover the pool (to reduce FC loss from UVs and reduce evaporation), and leave the pump running on a timer (prevents FC dead spots). If someone can add a jug of bleach on Sunday, or so, that would be good, the pump should be running when they do.

    ** Time to creat a sig. Go to User Control Panel, the Profile, then Edit Signature. We need to know:
    1) The size of your pool in gallons
    2) The type filter you have (sand, DE, cartridge)
    3) If your pool is an AG (above ground) or IG (in ground)
    4) If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
    5) If you know, tell us the size pump and the size (flow rate) of your filter.

    Plus any other related pool equipment.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

  12. Back To Top    #12

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    Re: Black algae

    Don't have a cover but can take care of all else.
    Thanks
    15000g Gunite
    48sqft DE Filter

  13. Back To Top    #13
    frustratedpoolmom's Avatar
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    Re: Black algae

    Do you have an autofill feature? How do you prevent the pump from running dry?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

  14. Back To Top    #14

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    Re: Black algae

    No problem it runs wth a timer. Friend can check make sure it is OK. I usually do not have to add water more often than q 2 weeks.
    I will send you the numbers when I get my F100.
    Water is beautiful with 3 days of your advise.
    Hope I can defeat the BA.
    15000g Gunite
    48sqft DE Filter

  15. Back To Top    #15

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    Re: Black algae

    Just got back after a week in Alaska with my boys. Alaska was unbelievable. My pool looks fantastic too. Got the F100 test kit and used it this am.
    Here are the results
    FC 4.5
    CYA 80 approx
    pH 7.5
    CC 0
    TA 80
    Remember, pool volume 15000
    Based on the calculator I should shock to 21 ppm and keep the FC at 7-9.
    Is it safe to swim at that level? I can't empty pool now to lower the CYA and now that i got rid of the pucks and powder shock shouldn't it gradually come down as I replace the water that evaporates? Or does evaporation just concentrate the CYA more? What should I do as maintanance to keep the beast out? Would once a week bristle brushing do?
    Thanks for all your advise, my pool has never looked this good and I think I defeated the beast BA.
    15000g Gunite
    48sqft DE Filter

  16. Back To Top    #16

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    Re: Black algae

    Quote Originally Posted by data9798
    Based on the calculator I should shock to 21 ppm and keep the FC at 7-9.
    Is it safe to swim at that level? I can't empty pool now to lower the CYA and now that i got rid of the pucks and powder shock shouldn't it gradually come down as I replace the water that evaporates? Or does evaporation just concentrate the CYA more? What should I do as maintanance to keep the beast out? Would once a week bristle brushing do?
    Yes, it is fine to swim @ 7-9ppm. I also swim in my pool when it is at shock level......others do not.

    The CYA will not evaporate. Drain and refill is your only option.

    Maintenance? Keep your4 FC up. Never let it get below 5ppm or so.

    Brush, backwash as necessary, etc. Simpll practice good pool management but above all else, keep the FC up where it belongs.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  17. Back To Top    #17

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    Re: Black algae

    All year pool sparkling clean. This spring lost of oak pollen and leaves and brown spots (not round) all over a shallow area. They disspaear with granular chlorine but come back next couple of days. Is it black algae or tanins from Oak trees debri?
    pH 7.6, FC 5, Cya 30.
    15000g Gunite
    48sqft DE Filter

  18. Back To Top    #18

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    Re: Black algae

    Since they disappear with FC, they are likely tannin. Bring your FC up to around 8-10ppm and hold it there for a week. That will almost surely remove all organic staining like tannin.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  19. Back To Top    #19

    Re: Black algae

    I've found that with a few pools that I've had to control BA, just by keeping the FC up (proportional to the CYA) it fades away over time (4-6 weeks).
    ~45Kg Pool with attached Spa, NSP-72 DE, Minmax 400 Heater, Tahoe Blue Pebbletech, Jandy SWG via Aqualink RS-8, The Pool Cleaner (black)
    Pumps: X3 Hybrid Pump (switches to SPA), 2HP Spa (additional, when SPA is on), and a 1HP For Waterfall
    8, 4x12 Solar Panels on the roof of the pool-house (~12' up)
    CAPTAIN JAMES T. KIRK: "I'M SORRY. I CAN'T HEAR YOU OVER THE SOUND OF HOW AWESOME I AM" (Thanks to TFP!)

  20. Back To Top    #20

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    Re: Black algae

    It seems that using liguid shock or bleach the pH tends to go up and require quite a bit of muriatic acid to keep it at 7.6. And after a while the TA goes down having to add Baking soda. Is this so? Am I doing somthing wrong? BTW spots fade away immediately when I add bleach and FC above 5. Still getting pollen at this time of the yr in south texas.
    15000g Gunite
    48sqft DE Filter

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