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I keep getting algae on my pool walls, even 1-2 days after a shock. The rest of the water looks good and clear. Any ideas? Getting a test kit today, what chemicals are likely causing the problem?

By June 5, 2019 11 Comments

I keep getting algae on my pool walls, even 1-2 days after a shock. The rest of the water looks good and clear. Any ideas? Getting a test kit today, what chemicals are likely causing the problem?

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  • decaturbob says:

    do you have a filtration system running and checking the chlorine levels consistently?

  • Papalyjon says:

    When treating algae in your pool, you really need to brush the walls and super chlorinate. Algae will return even after heavy shocking because biofilms in your pool form a protective coating that chlorine and algae killers won’t easily penetrate.

    Make sure your pH and alkalinity are well adjusted, because when it is, your chlorine is a more effective sanitizer (due to hypochlorous acid being the active species).

    Also use an algae killer while treating. Now your water might turn cloudy as dead algae floats off.

    Run your pump 24/7 and clean the filter daily until the water turns clear. Vacuum the pool by sending the water to waste if you want to quickly clean dead algae from the floor. This will reduce the chlorine demand of your water, because there’s less biological material for hypochlorous acid to needlessly attack. If the water is cloudy, use a flocculant to quickly settle the dead algae for vacuuming.

    Once clean, adjust the water chemistry again and use an algae preventative for good measure.

    I cleaned pools while in school. Also, visit a hardware or pool store. They usually do free water testing and the chemical vendors tell them how to treat different situations. They’re usually pretty helpful and friendly.

    Good luck!

  • kcornet says:

    I’m seeing the same problem. All of the rain we’ve been having just keeps adding nutrients to the pool water.

    Keep your pH correct, and keep your chlorine levels up. Run your filter a lot. Don’t backflush your filter until the flow through the system is greatly reduced. A somewhat dirty filter is a better filter than a clean filter.

  • ronocnikral says:

    Buy a DPD test kit. Switch to bleach. Use the TPF SLAM [https://www.troublefreepool.com/blog/2018/12/12/slam-shock-level-and-maintain/](https://www.troublefreepool.com/blog/2018/12/12/slam-shock-level-and-maintain/) Anyone telling you to use an algaecide, although with good intentions, does not know what they’re talking about. Save your money, have people at walmart think you’re trying to clean up crime scenes.

    Source: pool owner and do water treatment for my joejob.

  • upstateduck says:

    go to “pool school” [shock levels need to be maintained for awhile for it to be effective]


  • I_am_Bob says:

    When is the last time the sand in the filter was replaced?

  • lvex0101 says:

    A lot of folks believe a properly maintained sand filter should rarely, if ever, actually need replaced because of its nature. If you choose to do this yourself, be careful as its easy to damage the arms at the bottom of the reservoir. I use an annual filter cleaner that has served me well. whatever is top reviewed on amazon has been my choice.

    As others have mentioned, you are going to need to make sure you have sustained shock and lots of filtering to get rid of it. I just recently went on a two week work trip and came back to a green pool. Steps for me were as follows.

    Scrub thoroughly with pool brush,
    5x normal amount of shock (I use one bag weekly typically),
    Run filter for two days straight,
    Add clarifier,
    Run pool overnight,
    Scrub a dub,
    Vacuum bottom of pool to waste a few hours after the filter kicked off (allowing junk to settle at the bottom),
    2x shock,
    Run filter for two days straight,
    Regular shock,
    Add clarifier,
    Back to routine

    The first backwash yielded lime green
    The second backwash yielded mildy green

    I haven’t had any issues since and I’m back to perfectly clear. My methods may not be perfect but they work for me.

    Note: do not depend on the clarifier for clarity. It helps, but if you constantly have to use it you have bigger issues. I use it for its ability to bind very small pieces of matter that can then be caught by the filter or sink to the bottom of the pool to be vacuumed.

  • Bungeesmom says:

    Make sure you wash your swimsuits after swimming at another pool, Ocean, lake, etc.

  • wg5386 says:

    Algicide needed not more chlorine.
    I used True Blue 6 in 1 its chlorine with stabilizer and algicide already mixed in. Makes it much easier to keep the pool looking clear and reduced the amounts of random chemicals ive purchased by a lot.

  • drnick5 says:

    Former pool pro here
    First, what color is the Algae? I’ll assume its green (which is the easiest to get rid of) pink and black are FAR worse.

    What type of shock are you using? (Liquid? or granular?)

    If its liquid, make sure its a high percentage and not something you bought at a discount store. (I’ve see 1 gal bottles of liquid shock that are almost entirely water… so while its cheap, it does nothing).
    You’re best bet is to get a 5 gal bottle of liquid chlorine from a local pool place, depending on your pool size, this will give you a few treatments.

    When you shock the pool, you ALWAYS want to do it at night, once the sun is off the pool. Once you throw the shock in, you need to brush the walls to get the algae into the water so the shock can work to kill it. You’ll want to do this a few times, brush it, come back in an hour or two and brush it again.

    I’d probably also suggest using an algacide. since you currently have Algae, you’ll want to use somethig like an algacide 60, or somethign that has a little bit of copper in it. this will work with the chlorine to help kill it.

    Once its gone, you’ll want to get some concentrated Algae preventative. This stuff only requires you to jump in a few ounces once per week. But will help keep it away.

    You need to check your chemical balance, the most important ones are chlorine level, PH and alkalinity. If you’re PH is way off, the chlorine won’t be nearly as effective. Generally you want it in the 7.2-7.6 range

  • MaconShure says:

    I read last night that you should shock a pool late in the day/evening because the sun will drive off the chlorine. The site also suggested addressing pool with with adjusting alkalinity first, chlorine and then pH. Remember it as treating your pool alphabetically.

    BTW, I was looking at Walmart and they have a big box of baking soda in the pool section. Figured the price per pound and at Aldi’s it’s half as much per pound but comes in one pound boxes. I read that soad ash is better but can’t confirm.

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