Algae in gunite pool

I am taking over a new pool thats been done for about a month.  Got most of the dirt out, now I have a lot of greenish black algae on the natural stone walkin and some on the finish.  Will not brush up.  What is a good method to removing it?


We are a vinyl liner/ Fiberglass company and I have never done a gunite finish, so any help that you can give me I really do appreciate it !

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  • Chris

    I'm curious. Why did the pool turn? Did the pool/plaster contractor not provide a start up for the homeowner?

    On new plaster start ups the first 24-48 hrs are very critical in balancing the water to ensure a lasting plaster finish. Even up 30 days after application when it's fully cured.

    For your sake, I hope the company that plastered won't point the finger at you in case of a failure. Unless you have some history of the past month's chemical routine, brushing, vacuuming, etc.. you may become responsible.


    Test and balance ALL the chemicals in the pool before you blast it with chlorine. Check your fill water too as it may have an impact on your ability to balance the water.

  • I agree with Rob; shock to 15 ppm chlorine (or higher, depending on all water parameters).  I would use only liquid chlorine, as you are only adding water, chlorine and a little salt to the pool.  This allows you to control the water better.


    Sounds like black algae to me.  You can beat it, bit it is gonna take some time!



  • Shock to about 15ppm chlorine. Be sure to use an unstabilized product though (bleach or cal-hypo) and if you go with cal- hypo be sure to dissolve it in a bucket first, as it has the potential to degrade the plaster finish if it just sits there undissolved.


    You could also try a monopersulfate shock, but that can cause false high combined chlorine readings


    As a last resort, I would use a non-copper based algaecide, being sure to add it during the sunniest part of the day.

    I've cleaned up some really nasty pools and from what I've found, algaecides are never necessary if you can keep your CYA is below 30


    Good luck

    EDIT: advise the owner to switch to bleach or cal hypo as their primary method of chlorination once their CYA hits the 30-50 range or else it will totally debilitate the potential of their chlorine and cause more algae!

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