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Thread: Large black algae outbreak help

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    Large black algae outbreak help

    OK I need some serious help for a serious black algae problem. My parents purchased a house with a pool several months ago. The pool was pea soup green when they moved in. Thanks to TFP and a FAS test kit I have managed to get the water crystal clear and all parameters back in range. The problem is the pool is approx one third covered in black algae. We have been brushing daily or every second day and keeping the chlorine at a slightly elevated level for at least the last month but it just does not seem to be clearing up or so it seems. Is there something else we can do or do we just persevere with the brushing and keeping the chlorine slightly higher. I have enough managing my own pool let alone the parents as well.

    Pool is very similar in volume and surface to my own pool but here are the exact details.

    Pool volume 50,000L
    Surface Pepplecrete
    salt water with a salt water chlorine generator.

    Water Parameters
    FC: 5
    CC: 0
    pH: 7.4
    T/A: 120 (SWG booklet recommends 90-150)
    Calcium:300 (SWG booklet recommends 300-350 for this pool surface)
    CYA:60 (SWG booklet recommends 40-65)
    Salt:5600 (SWG booklet recommends 5000-6000)

    I know chemicals for treating black algae are not recommended but is there some way to get this under control.
    15.8K gallons (60K Litres), IG, pebble, Davey 1hp 300lpm, sand filter, K Chlor SWG, Kreepy Krauly.

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    Mod Squad YippeeSkippy's Avatar
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    Re: Large black algae outbreak help

    Have you SLAM'ed the pool at all during this time? Your FC is at bare minimum level for your CYA if the pool was free of algae, but you need so much more to kill off the algae once you have it. Have you read the Pool School (button at the top right of this page) article on how to SLAM a pool? Its a matter of bringing the FC up to a specific level (based on your CYA) and *maintaining* it at that level until the algae is dead and gone. Its *not* a one-shot deal where you hear of folks just tossing in chemicals (often willy nilly, often unnecessary ones at that) and assume its fixed. It is a process. All that brushing you're doing will help a lot because it stirs up the algae and gets it into the circulation with all that chlorine. It also disrupts any biofilm coverage that is protecting the algae from exposure to the chlorine.
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    Patrick_B's Avatar
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    Re: Large black algae outbreak help

    Looking at this, lack of ample FC seems to be the problem. Just guessing, I would say the FC was never held high enough for long enough to kill the BA.

    It is especially hard to kill, and a FC of 5 at 60 CYA won't take care of it. Even if you killed some or most with a SLAM, it is taking hold or continuing to grow with the current 5 FC.
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    Butterfly's Avatar
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    Re: Large black algae outbreak help

    Yep, what they said ^^^^ Also, you should be brushing daily with a S/S brush. It will knock the heads off the BA and allow he chlorine in for the kill. Here's the scoop on the brushes, JIC you needed to know:
    Nylon is for vinyl, fiberglass, tile, and plaster that is less than one year. (Plaster includes any exposed aggregate and marcite finish, btw!) Combo brushes are for older plaster. All stainless are for algae (very stubborn green algae and also the ONLY brush for black algae.)

    You CAN unscrew the Wall Whale from the nylon brush it comes with and screw it on a combo brush if your plaster is over a year old. Newer plaster is really too soft for anyting other than a nylon brush.
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    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

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    Re: Large black algae outbreak help

    Yes SLAM'ed the pool when the parents first took over and it cleared the water to crystal clear except for the black algae which we could not see till the water was clean. The SWG had a recommended FC of 1.5 to 2ppm so I had figured 5 should be doing something to stop the black algae. We are adding liquid chlorine on top of running the SWG to maintain that level. How long should the SLAM be continued for. Maybe we stopped too soon as once the water was clear.
    15.8K gallons (60K Litres), IG, pebble, Davey 1hp 300lpm, sand filter, K Chlor SWG, Kreepy Krauly.

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    Patrick_B's Avatar
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    Re: Large black algae outbreak help

    Yes, you stopped too soon most likely, but the low level of FC afterward allowed it to grow again. Industry and Governments do not take Cya into account when they suggest "recommended" Chlorine levels. I would first complete a SLAM again and make sure you pass all three criteria. If you can, doing it until the BA is all killed would be ideal. As Butterfly mentioned, brush it often to expose the BA fully to the FC so it can kill it. If you are still swimming down there, you can swim up to SLAM level per your CYA level, but not higher. Just remember, you should turn off the SWG before you perform the OCLT. You will have to be diligent about adding Chlorine often, especially after a swim.
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    Re: Large black algae outbreak help

    Normal chlorine levels will not kill black algae that is already established, especially if you do not scrape off their heads with a stainless steel brush. Normal chlorine levels as specified in the Chlorine / CYA Chart will prevent green and black algae growth if not already established. So you need to SLAM the pool and use a brush to knock off those heads (sticky slimy surface layer that is chlorine resistant) to expose the roots of the algae to high chlorine levels.
    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: Large black algae outbreak help

    Black algae is the most commonly mistaken form of algae. Not saying you don't have it, but how did you determine it was Black Algae?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Large black algae outbreak help

    Quote Originally Posted by duraleigh View Post
    Black algae is the most commonly mistaken form of algae. Not saying you don't have it, but how did you determine it was Black Algae?
    Yep pretty sure it is black algae dark almost black spots/ large sections of pool walls and to a lesser extent the floor of the pool. Dark green when scraped off and squished. Looks like I will be stocking up on chlorine and doing the SLAM again. Weather is starting to cool down in OZ so it might help with chlorine loss due to sun
    15.8K gallons (60K Litres), IG, pebble, Davey 1hp 300lpm, sand filter, K Chlor SWG, Kreepy Krauly.

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    Patrick_B's Avatar
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    Re: Large black algae outbreak help

    If it's more cloudy it will help, but do stock up, you'll need plenty. Alga doesn't like cold, but you won't see the dramatic growth reduction we do up here in winter.
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    Re: Large black algae outbreak help

    I agree, it sounds like black algae.

    That stainless brush will do you as much good as the chlorine but they must be used together.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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