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Thread: Black algae question for experts

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    HardTrance9's Avatar
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    Black algae question for experts

    Hi all, haven't post in a while but keep reading when I can.

    We took over a pool almost 18 months ago or a little more. First, it had black algae on the walls, not much, but it was obvious and present, but more important,
    it didn't matter how many times we brushed (with nylon or metal), or if we raised the chlorine level (not to shock level though), the algae wouldn't dissapear.

    The pool has some sort of pebble finish, but it is not smooth, so algae is able to "hide" intho those places where the brush can't reach.

    So, the story is that we drained the pool (CYA leve was like 180+), we shocked the pool (normal algae levels), with the brushing and vacuuming process and in the end
    it took 18 months (until now) for the black algae to come back.

    It is back and much stronger as it was not possible to perform the shocking for a while and the pool was "very" busy all the time (many guests in and out for some months).

    Black algae is worse and looks like a stain on the walls now. Very hard to get off. So finally we have the time and chance to do the super shocking level. The CYA was too high again, so pool has been already emptied out giving the following readings:

    FC: 0
    CC: 0.5
    pH: 7.2
    CH: 40
    TA: 70
    CYA: 30
    salt: 560

    It is a SWG and it is an 11,100 gallon pool with a not that big sand filter (yeah, I know, bigger is better but owners will change it someday).

    The pool calculator says the mustard algae is 19 but here are my questions:

    1) Is mustard algae considered as strong as the black algae?

    2) That black algae is very hard, so we are really considering in using double the dose and keep the FC at 40. How does this sound to you?

    3) We will do as possible a two time check a day, with brushing, but the question here is: do we have to vacuum everyday? or just every other day?

    4) We will back wash the filter also from time to time and keep the pump 24/7. Is this ok or the pump can be set at a different schedule? The pool is not that green, just a little for now.

    Any advise will help.

    Two other options were considered before, but they were to expensive for now:

    a) Re do the pool with tile (small blue squares)

    b) Acid wash the pool

    Cheers to all!

    Saludos

    Hector
    In charge of some SWG and Bleach pools... still a newbie..

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    Re: Black algae question for experts

    One thing that I found that really helped on black algae spots was rubbing a 3" trichlor tablet on the spots. I bought a little gadget that holds one on the end of the pole to use on the ones that couldn't be reached under water. If I remember right it was about 25$ or so and the name of it is algee-gone and it is made by pentair. That is not a mispelling It is worth every penny and you are hitting it right on the spot. If you have any trouble finding it online let me know and I will look up where I got it. Don't forget to figure in the little bit of cya you are adding with the tabs. It's not alot, just keep it in your calculations.
    10,800 gallons Gunite/Plaster
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    HardTrance9's Avatar
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    Re: Black algae question for experts

    Quote Originally Posted by Dalandlord
    One thing that I found that really helped on black algae spots was rubbing a 3" trichlor tablet on the spots. I bought a little gadget that holds one on the end of the pole to use on the ones that couldn't be reached under water. If I remember right it was about 25$ or so and the name of it is algee-gone and it is made by pentair. That is not a mispelling It is worth every penny and you are hitting it right on the spot. If you have any trouble finding it online let me know and I will look up where I got it. Don't forget to figure in the little bit of cya you are adding with the tabs. It's not alot, just keep it in your calculations.
    Sound good! Thanks for the hint! We can get it down here in Baja I think but will look for it. Thanks for the offer too
    In charge of some SWG and Bleach pools... still a newbie..

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    Re: Black algae question for experts

    Even though it's not really recommended by most of the people on the board. I have had success with black algae treat from united chemical. It did take care of it rather quickly but it also did screw up the chemicals for almost an entire season (it basically made the pool into a bromine sanitized pool) Which is hard to keep track of due to it's weakness towards UV. I'm only giving this option if you exhausted all others.
    -Kevin
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    22,000 gal / 16' x 32' / Vinyl / Hayward s244t /Pentair SuperFlo 1 hp

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    Re: Black algae question for experts

    Black algae is in between green algae and yellow/mustard algae in terms of the chlorine level needed to kill it, but that is for planktonic (free-floating) algae. Black algae forms a waxy surface layer that protects the interior from chlorine attack so it is critical to brush off that surface layer to expose the lower depths to chlorine. Having an uneven surface has made that difficult for you. Rubbing the Trichlor pucks on the affected areas right after strong brushing might help.

    I suspect that the circulation in the pool is poor or that the chlorine level got low for too long. The normal SWCG rule of an FC that is around 5% of the CYA level is probably too low if black algae is already present. Black algae is usually only seen in pools that have too low of an FC/CYA ratio for too long.

    I don't know if borates help against black algae, but that is something you could try and it won't have the side effects of bromine/bromide or copper. Polyquat would be another option, also without significant side effects.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Black algae question for experts

    I have had success with black algae treat from united chemical. It did take care of it rather quickly but it also did screw up the chemicals for almost an entire season (it basically made the pool into a bromine sanitized pool) Which is hard to keep track of due to it's weakness towards UV.
    For me, that's too many unintended consequences to consider that as a viable alternative.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    HardTrance9's Avatar
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    Re: Black algae question for experts

    Hi all,

    We are still going through the process. Two daily thorough brushes a day with daily readings on FC.

    We were only using liquid chlorine but chlorine got consumed right away.

    We had a CYA of 30 after draining the pool so I decided to use some pebble trichlor to make the chlorine level hold more.
    First time we raised the FC to 45 only with liquid chlorine at 5.25% and next day the FC was 2.

    So used some granular trichlor (1.8 kg aprox), raised the FC again to 35 aprox with liquid chlorine and FC same day afternoon was 15. Yesterday we raised it again to FC 25.

    Today in the morning the reading is FC 8.5. Checked on the CYA today (cause using the trichlor small "balls" are supposed to raise a little CYA), but the CYA stayed at the same level
    28-30. Don't know if this reading can also be bogus cause of the high chlorine just as it happens with the pH readings when shocking the pool?

    So we are adding today 8 liters of 6% liquid chlorine to raise the FC to 20 again and brush and vacuum.

    Saludos!
    In charge of some SWG and Bleach pools... still a newbie..

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