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Thread: Oxalic Acid - Sock Treatment?

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    Oxalic Acid - Sock Treatment?

    My pool is a five year old pebble-tech with several rust spots in various areas. Main cause of rust spots are the kids throwing various metal objects in pool (nail, nuts/bolts, etc.)
    Aren't kids grand?

    I have an IC40 SWG in use and currently the pool is crystal clear. I also use a newly installed Zodiac MX8 which so far has been kicking butt. (Doesn't interfere or get hung-up with the in-floor pop-ups)

    I have been reading quite a bit about rust removal and it appears (if I'm understanding correctly) that using Oxalic Acid in a sock would have many advantages over Ascorbic Acid. The chief being that Oxalic breaks down into CO2 as opposed to an insoluble organic compound like Ascorbic. I've also read that Oxalic removes the rust better due to its enhanced iron absorption properties.

    My tentative plan is to put the Oxalic acid (99% pure) into a sock and cover with a brick over the respective stains.

    My question is this - Does this sound like a better idea than the Vitamin C in a sock?

    I was thinking that I would stick with the Oxalic because I can pick up a 50 pound bag for around $80 bucks and that it would also be beneficial as a calcium reducer (hard water here in Phoenix) as well as a PH reducer.

    Penny for your thoughts?

    Thanks!

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    Poolkim's Avatar
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    Re: Oxalic Acid - Sock Treatment?

    I had a rust spot in the bottom of my SWG Fiberglass pool and I just took a lemon to those spots... used it as a scrubber... worked great... not sure what a pebble tech pool is made of but it's worth a try.

    Good luck!
    9800 Gallons IG Fiberglass
    Cartridge Jandy CT100
    SWG Jandy Apure700
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    Re: Oxalic Acid - Sock Treatment?

    Quote Originally Posted by Poolkim
    I had a rust spot in the bottom of my SWG Fiberglass pool and I just took a lemon to those spots... used it as a scrubber... worked great... not sure what a pebble tech pool is made of but it's worth a try.

    Good luck!

    Did you empty it first? My pool is full and I'm in the swing of summer as you can imagine and have no intention of emptying it!

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    solarboy's Avatar
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    Re: Oxalic Acid - Sock Treatment?

    I did that with Oxalic. In a sock it worked great; like an eraser. Then I made the mistake of spooning in the powder to tumble down the wall over a stain. I did this about 8 times and reached some critical level of oxalic in the water and all my Calcium combined with the oxalic to form Calcium Oxalate. The pool went white and took about 4 days to clear.
    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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    Poolkim's Avatar
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    Re: Oxalic Acid - Sock Treatment?

    No, I didn't empty the water. I just swam to the bottom with goggles on and used the lemon like a scrubber.
    9800 Gallons IG Fiberglass
    Cartridge Jandy CT100
    SWG Jandy Apure700
    Max HP pump

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    JasonLion's Avatar
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    Re: Oxalic Acid - Sock Treatment?

    Ascorbic Acid is much easier to work with and has fewer problems. Oxalic Acid can work better sometimes, but AA works well enough.
    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 - Sock Treatment?

    Quote Originally Posted by JasonLion
    Ascorbic Acid is much easier to work with and has fewer problems. Oxalic Acid can work better sometimes, but AA works well enough.
    Would the Oxalic be suitable for lowering Ph or would the possibility of calcium oxalate forming be a problem? I was reading that the ascorbic breaks down and leaves organics that don't get filtered out.

    Thanks.

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    solarboy's Avatar
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    Re: Oxalic Acid - Sock Treatment?

    When my calcium precipitated out, my pH had dropped from 7.5 to 7.0. I'm not sure how much oxalic acid I added though, my guess is around 8 oz.
    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 - Sock Treatment?

    The organics left over from AA are completely harmless.

    Both AA and oxalic acid will lower the PH, though not as much as muriatic acid or dry acid would.

    Calcium oxalate can be a problem. There are ways of dealing with it, but that makes the whole process more complex.
    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 - Sock Treatment?

    Quote Originally Posted by JasonLion
    The organics left over from AA are completely harmless.

    Both AA and oxalic acid will lower the PH, though not as much as muriatic acid or dry acid would.

    Calcium oxalate can be a problem. There are ways of dealing with it, but that makes the whole process more complex.

    Would this be a potential upside? I currently have a CH of 450+ PPM (hard water plus using TriChlor for a couple of years) Would it be worth having the extra Calcium precipitate out and therefore reduce my total CH after backwashing? Or am I missing something?

    My other thought on how to remove the extra CH and reduce the TDS level would be to buy a high capacity RO system that I could use to filter the water that way. (Maybe it's overkill though)

    Thanks.

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    Re: Oxalic Acid - Sock Treatment?

    There are calcium reduction products on the market and they might use sodium oxalate though I don't know (they might use fluoride which would reduce both calcium and magnesium). See this thread for what happened to one of solarboy's maintained pools as he mentioned above.

    The problem is to make sure that the precipitate doesn't adhere to pool surfaces, but it sounds like it wouldn't (unlike calcium carbonate), but does create a bit of a mess that takes time to clear. This is one situation where a clarifier might clear the pool faster, but then again it might not since calcium oxalate isn't like negatively charged cells or other materials.

    The good news is that any excess oxalic acid (or oxalate ion) in the pool is readily oxidized by chlorine to carbon dioxide so nothing remains. As Jason noted, however, using ascorbic acid will have dehydroascorbic acid (or dehydroascorbate), but that is very soluble in water and does not further react with chlorine so is not a problem. For a full pool treatment, ascorbic acid can be used, but doing that with oxalic acid would cause a lot of cloudiness and precipitated clacium as solarboy experienced.
    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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