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Thread: Black algae, chlorine and ammonia

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    Join Date
    Aug 2012
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    Fort Worth, TX
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    Black algae, chlorine and ammonia

    I have what I believe are black algae spots on the bottom of my pool.
    It is 15,000 gal., in ground plaster.

    I found a prescription on the internet that calls for putting 8 gal of liquid chlorine in it followed by 2 gal of ammonia hydroxide.

    The claim is that this is the only way to completely get rid of it. It will supposedly burn the algae out, roots and all.

    1. It does not specify the size of the pool. I wonder if mine would require less.

    2. It sounds dangerous to me. We're constantly told not to mix ammonia and chlorine, due to the fumes given off.

    Has anyone ever heard of this? Will it work? Is it safe?

    I just signed up to ask this question, do not have the type test kit required. I will purchase one and post the results, If this will help

    Thank you.
    10,000 gal / Plaster / Cartridge Filter / 1 1/2 HP pump motor/ TF-100 test kit.

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    duraleigh's Avatar
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    Re: Black algae, chlorine and ammonia

    Chlorine kills algae. Ammonia consumes chlorine voraciously. Putting them both in the pool makes no sense.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Black algae, chlorine and ammonia

    Steel wire brushing the algae with a black algae shock level is the only realistic way of removing black algae - are you sure it is black algae? I'm with Dave adding an ammonia based product will only consume chlorine and allow the spore good conditions to multiply.

    Black Algae needs to be knocked apart with a steel wire brush and chlorinated heavily to kill.
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Black algae, chlorine and ammonia

    I appreciate your reply.

    No I am not sure it is black algae.

    It looks like the descriptions I have read. The spots are mostly round. There are a few that are elongated smudges.
    I'm going to dive into it today and see if it will scrape off and if it appears to be an algae rather than a stain.
    10,000 gal / Plaster / Cartridge Filter / 1 1/2 HP pump motor/ TF-100 test kit.

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    Re: Black algae, chlorine and ammonia

    If it scrapes off try bringing a decent amount out of the pool with you for analysis, using a bucket helps.

    There are plenty of good descriptions online to help you ascertain if you really do have black algae or not.
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Black algae, chlorine and ammonia

    The chlorine + ammonia approach is to produce monochloramine. That is mostly to get around high Cyanuric Acid (CYA) levels since high CYA lowers the active chlorine level, but doesn't affect monochloramine. This is similar to adding sodium bromide to create bromine since that is also not affected by CYA. Both approaches are unnecessary if one keeps their CYA level in check and keeps their Free Chlorine (FC) level up high enough relative to CYA.

    Just raise the FC to shock level for your CYA level and use a brush to scrape off the waxy head of the black algae to expose the lower layers to the high chlorine level.

    If it's really black algae, then if you scrape some off and take it out of the pool, wipe it on a white piece of paper. If it looks dark green when smeared, then it is indeed black algae.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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