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Thread: Oxalic Acid to Treat Fungas on under side of a gunite pool

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    Oxalic Acid to Treat Fungas on under side of a gunite pool

    I have ben fighting this stain issue for 2 years.. I have tried everything like vitamin A etc.. My local pool store guys thinks I have a fungas on the under side of my gunite pool due to poor drainage from a clay base... Thanks NJ...

    He told me to use Oxalic Acid in the pool and to also mix and poor the solution as close to the base of the pool around the outer edge. Where is the best place to find Oxalic Acid and how much do I mix in water for the treatments. HELP !!!!

    I have a 30,000 gallon gunite pool with a quartz 3M finish in the plaster.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    At the pool store.

    Oxalic acid is found in products that remove iron stains, you'll probably find it in powder form in a little pouch that you place on the stain.

    It's also found as deck or wood cleaner at the hardware store (may be mixed with other chemicals, may be in liquid form), or at the grocery store in the cleaning product area (Bar Keeper's Friend is such a product). Again these may include additional chemicals that are not suitable for pool use and such the quantity for pool use cannot be determined.

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    JasonLion's Avatar
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    What is the symptom that you are trying to treat?

    Fungus underneath the floor of a gunite pool wouldn't make any difference. It would not be able to get through the gunite and nothing would be affected by it.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    The symptom I have is a light Brown stains that get worse every year and sems to spread around the pool. I put a chlorine tab on the stain as a test and after a while is does make it go away. Am i barking up the wrong tree?
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    solarboy's Avatar
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Be very careful with using too much OA. I recently had an unsettling experience when I added too much. I'd only use it in a sock as a "sponge" to wipe affected areas.
    oxalic-acid-treatment-and-calcium-oxalate-worries-t32659.html?hilit=oxalic
    Self built 5500 gallon bare concrete (temporarily) pool with limestone coping, Pentair Swimmey 1/2 HP pump, Triton sand filter with DE, Simpool peristaltic muriatic acid pump with pH sensor and Monarch SWG. Home made solar heater with Pentair Compool control panel and 3 way valve. 1 skimmer, 1 main drain, 2 returns, 2" plumbing, Hayward auto fill valve.

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    JasonLion's Avatar
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Try holding a vitamin C tablet against a stained area for 30 seconds and see if that does anything.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    I tried a vitamin C bag and it did not effect the stain. The chlorine tablet did effect the stain.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Then the stains are organic and you are chronically not maintaining enough chlorine in the pool. Bring the chlorine up to adequate levels and the stains will eventually go away. Post a set of test results and we can help get you started.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    I just had the water tested yesterday when I spoke with the local pool guy.. Chlorine is adequate and i tend to run it on the highside.

    PH 7.3
    Free Chlorine 7.0
    Alkalinity 110
    CA 150
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    The chlorine tablet did effect the stain
    Did it lighten or remove it?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    No change. the stains get worse every year. I also use liquid shock and used 3 gallons last weekend.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    sorry I misunderstood the question... it lloks like it removed the stain where I haave the tablet.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    If the puck lightened the stain, then the stain is organic and chlorine will eventually remove or lighten it. Keep your FC right where it is continuously (don't let it drop) and brush the stain often. I think you will see improvement in a week or perhaps sooner. It is fine to swim at the current FC of 7ppm

    Why did you shock?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Dear King,

    You need to get a very good test kit--either the TF-100 or the Taylor K-2006. You won't find these in stores. Look in Duraleigh's signature for the TFTestKits--click on the link. Get that thing on its way in the mail to you.

    In the meantime, read Pool School. Get a CYA test done on your water at the pool store, although once you get your own test kit, your results should be the results you trust.

    Good luck~~

    Lana
    23,600 gallon, refurbished 1960's inground concrete, Jandy sand filter w Jandy 2 hp variable speed pump, Pool Pilot Digital SWCG+Chemtrol 2100+CO2 tank; PebbleTec White Pearl with 10% Cobalt Blue Dark Beadcrete by Olympic Pool Plastering, Georgia. Taylor K-2006 Test Kit; Aqua Check Salt test; LaMotte borates test, and Jack's Magic Sequest test kit; SparklyPoolitis level: extremely high.

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    I shocked last weekend after heavy use from a holiday party. Is there some sort of super shock treatment I can use to promote the lightening of the stains? 4 years ago I had a guy come in a dump 16 gallons of muratic acid in and it did lighten the stains but they came back.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Is there some sort of super shock treatment I can use to promote the lightening of the stains?
    Yes. Chlorine. The stains didn't get there in 24 hours nor can you expect to remove them that quickly. Holding your FC up around 7-10ppm for a week will be simple and inexpensive.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Quote Originally Posted by solarboy
    I recently had an unsettling experience when I added too much.
    Sodium oxalate is packaged and commercialized as a CH reducer in Europe. As you noticed, it forms a precipitate (calcium oxalate) which is then vacuumed to waste.

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    solarboy's Avatar
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    Quote Originally Posted by CaOCl2
    Quote Originally Posted by solarboy
    I recently had an unsettling experience when I added too much.
    Sodium oxalate is packaged and commercialized as a CH reducer in Europe. As you noticed, it forms a precipitate (calcium oxalate) which is then vacuumed to waste.
    Yep I certainly noticed, I'd just spent a few coins on putting the CH in there ! It's only just redissolved in there.
    Self built 5500 gallon bare concrete (temporarily) pool with limestone coping, Pentair Swimmey 1/2 HP pump, Triton sand filter with DE, Simpool peristaltic muriatic acid pump with pH sensor and Monarch SWG. Home made solar heater with Pentair Compool control panel and 3 way valve. 1 skimmer, 1 main drain, 2 returns, 2" plumbing, Hayward auto fill valve.

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    Mod Squad Bama Rambler's Avatar
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    With a CYA of 150 (if I read that right) your min FC level should be in the neighborhood of 10 ppm.

    You need to drain about half of your water to get the CYA in range. Then you can keep the FC in the proper range to lighten those stains.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: Oxalic Acid to Treat Fungas on under side of a gunite po

    I did drain the water last year and lowered the CYA.. It came back up qucikly this year with the tabs I am using so I am now planning to us more frequent liquid chlorine and less tabs.. It is more work.. If the FC is in range how does the CYA affect the stains?

    Thanks for all of your great feedback everyone.
    20 x 40 gunite in ground pool, 400,00 btu Laars heater, 24" Hayward sand filter, 2hp Hayward Northstar pump, Hayward offline chlorinator

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