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Thread: Salicylic acid to remove iron stains

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    mraiteri123's Avatar
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    Salicylic acid to remove iron stains

    I have iron stains on my pool floor and walls. It's not heavy unless you clear it off and notice the bright blue diamond bright underneath. I thought all along it was algae stains from over time when algae got away from me. I finally took some advice and used vitamin C tablets or Ascorbic acid. It removed the iron stains and left large clear circles; so I know it is iron stains. My pool man is suggesting using Salicylic acid. It says they use it to clean rust off of stuff hit by well sprinkler system. Which is how I got the iron in the pool to begin with. He also says that if you use this you do not need drop the chlorine. Pool will stay balance

    Any ideas on using Salicylic. A friend of mine that worked for the city says just dropping PH will remove it. The acidic water will allow the stain to come off--maybe but I am betting that's time consuming.

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    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    Don't use salicylic acid. It's not just low pH from acid that dissolves a metal stain, but also needs to be a reducing agent that converts the iron from ferric form (Fe3+) to ferrous form (Fe2+) that is more soluble and then bound better by metal sequestrants. The reducing agent will react with chlorine (i.e. they counteract each other) which is why you want the chlorine low to start with or else you waste money on ascorbic acid that reacts with the chlorine.

    The reason salicylic acid is used to clean off rust is that it is an acid that is not too strong (it gets down to a pH of around 3) so is good for cleaning metal surfaces without causing too much damage. That is not what you want in the pool. You want a reducing agent and you want an acid and ascorbic acid (Vitamin C) is both.

    Follow the procedure in the Pool School article Metals in the Water and Metal Stains. We have gone through many pools with metal stains over the years and have tried a variety of techniques including other acids such as oxalic acid and citric acid, but ascorbic acid works best for iron stains (oxalic acid can be better for copper stains, but using too much when CH is high causes calcium oxalate precipitate as shown in this thread).
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    Re: Salicylic acid to remove iron stains

    Excellent post, chem geek!
    Dave S.
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    Re: Salicylic acid to remove iron stains

    Glad I ask--I only tried it in the spa ( clouds up nicely 0 and waited for your answer. I will read the pool school article and do it that way. Any recommendations on where to buy the Asorbic acid and under what name since i don't want to go back to the pool guy and tell him I can't do it his way. On line site? Also what sequestrant (flocc-right?) do you recommend. If i don't want to wait on chlorine to drop or to add the sqat60 ( sp??) to prevent aglae growth, can I just add more asorbic acid? Do you recommend vaccuum to waste or use the Flocc to filter? I know it recommend Ph at 7.0 but what is too low?
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    I will read the pool school article and do it that way.
    That should answer your questions.
    Dave S.
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    Re: Salicylic acid to remove iron stains

    Thnaks
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    Re: Salicylic acid to remove iron stains

    The Pool School article has a link to directions where that has links to a couple of sites for Ascorbic Acid though the links are old so the updated ones are PC NetwoRx (MSM Products) and The Chemistry Store.

    The Pool School article refers to several recommended metal sequestrants, all of which have HEDP. Metal sequestrants are not flocculants or clarifiers. They are chemicals that bind to metals so that they stay in solution and not re-stain. HEDP will slowly break down from chlorine so more will need to be added as a maintenance dose, usually a small amount weekly.

    The Polyquat 60 is sold in many products and I list some of them available from poolgeek.com in this post. This is an algaecide to prevent algae when the chlorine is at zero during the ascorbic acid process.

    Yes, you can use extra ascorbic acid to lower the chlorine level, but that's a waste of expensive chemical. If you want to lower your chlorine level more cheaply, you can use hydrogen peroxide where you put in your desired FC change into The Pool Calculator pretending you are adding chlorine and use 6% in the calculator pretending you are adding bleach. That same volume is what you would add using 3% hydrogen peroxide. If you instead use Baquacil Oxidizer which is 27% hydrogen peroxide, then put in 54% in the bleach % in The Pool Calculator and that's the volume of 27% hydrogen peroxide you would use to dechlorinate.

    The main reason we limit the pH to 7.0 is that the test kits don't read much lower, usually not below 6.8, so you can't really know how low you've gone. 7.0 works fine for removing metal stains and there is no need to go lower, especially when using ascorbic acid for iron stains.

    I don't understand the question regarding vacuum-to-waste or floc to filter. When you remove metal stains, you aren't precipitating anything. What you are doing is dissolving the rust and reducing the iron into soluble form that the metal sequestrant then binds to and keeps soluble in the water. There won't be any precipitate to vacuum up.
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    iron from well water is my problem.

    Hey it's me again--it seems like my problem all along has been iron in the water from a sprinkler system fed by well. I did use salicylic acid in just the spa and it cleaned the stains out fast--then flocc and vaccummed . TFP says don't use salicylic so I ordered the asorbic acid and the sequesting agent along with the algaecide recommended for the low PH. All Time I habe been blaming the aglae lookinjg stuff on the sides of the pool on my cya. I have it now way below 100. The stuff is still forming even though FC is way above 7. It looks like the light green stain on the wall . It brushes off easily. I have adjusted the sprinkler heads to minimize the water that can enter the pool but guess I will not get it all. Any new recommendations.. How to maintain pool if you get some well water from the sprinkler system. I know easy way is to turn off sprinkler but isn't there a recommendation to handle small amounts of iron.

    PS My pool water is crystal clear and has been all along. Just high FC and high cya and light green forming on sides of pool -- brushes off but it still forms--how can I prevent that.
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    The surest way to handle them is to maintain a level of sequestrant all the time.
    Dave J. TFP Moderator
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    Re: Salicylic acid to remove iron stains

    I have been to BBB many times but I do not understand maintaining a level of sequestrant at all times. What do you recommend and how much and how do you test for it. You are talking about Flocc right?
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    Not floc, Flocculent is a different animal. Metal sequestrant is a product made to keep metals in suspension. We recommend the ones made with phosphonic acid or derivitives thereof. There's an article on metals in Pool School.
    Dave J. TFP Moderator
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    Re: Salicylic acid to remove iron stains

    I ordered the kind that was recommended by TFP so it should be OK. I will read up more on this. Do I want to keep it in suspension so it doesn't stain the walls or so i can filter it out. Sorry just confused with the language. before all I did was keep it simple. Add chlorine, algaeside as the pool store recommmended.
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    You keep it in suspension. It is rarely if ever filtered out. You may get a little of it, but you'll never filter out 100% of it.
    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: Salicylic acid to remove iron stains

    I read up on it again and must not have been paying attention before. I will get some purple stuff and what is left in after I do the recommended treatment with the ascorbic acid I will keep some of the purple stuff in the pool. The real question is how much and how can you tell other than it is staining again. I appreciate your patience on this subject but man the pool companies all have such different ideas.

    One last question-Salicylic acid for the spa and just a few handfuls cleaned all the rust stains ( they looked like algae stains) off and the paster looks bite diamond blue again. I vaccumed the left over to waste . It worked so I must be missing something.

    It's two part question--how to tell the right amount of purple stuff (jack majic) and why not Salicylic acid . I am going to do it the TFP way just curious.
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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    Re: Salicylic acid to remove iron stains

    Quote Originally Posted by mraiteri123
    One last question-Salicylic acid for the spa and just a few handfuls cleaned all the rust stains ( they looked like algae stains) off and the paster looks bite diamond blue again. I vaccumed the left over to waste . It worked so I must be missing something.

    It's two part question--how to tell the right amount of purple stuff (jack majic) and why not Salicylic acid . I am going to do it the TFP way just curious.
    Any acid that lowers the pH can help to remove the metal stain, but without a reducing agent the form of the iron will not bind well to metal sequestrants so can re-stain when the pH goes back up. You could have used dry acid (sodium bisulfate) and accomplished the same thing, but the iron wouldn't be in a form that would prevent re-staining.

    After you removed the stains in the spa, did you try raising the pH again to see what happened? A spa tends to rise in pH due to aeration so is most prone to staining (depending on spa surface) if there is metal in the water.
    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
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    Re: Salicylic acid to remove iron stains

    Got it --you are right--iron stains come back some and guess they will. Just waiting on materials to come and now I understand.
    10K gal, IG gunite, Installed 2000, 1 1/2 HP pump, sand filter, Aqua Pure Digital 35 K gal SWG, Haywood Cleaner

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