Iron Stains and Oxalic Acid

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robertwo

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Jun 6, 2010
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Hi all, new to this forum. I'm located in France and need some help with a pool with a vinyl liner that has turned brown. I think, but can't be 100% sure that the stains occured when I was welding and grinding a few days ago and think that the iron grindings have probably blown in to the pool with the wind.

All the white PVC fittings, the liner and the fibreglass steps have turned brown and shock chlorine and scrubbing has done nothing.

I lowered the water level and managed to clean the top step and the skimmers and return jets plus about 10" of the liner above the water using a liner cleaner which I think was a 5% solution of Sodium Hydroxide (Caustic Soda).

I tried adding Vitamin C tablets on to the 2nd step below the water line and 4 tablets removed a fairly large area of the brown stain in a few minutes so I assume that it is Iron stains rather than organic staining.

I have been searching the internet for solutions and it seems that either Oxalic Acid or Ascorbic Acid will work since the Vitamin C tablets worked so quickly.

I am going to have to go with the Oxalic Acid as this is readily available and about a 1/5th of the price of the Ascorbic Acid in France. 80 Euros for 25Kg compared to 550 Euros for 25kg of Ascoric Acid.

What I need is a step by step guide to using the Oxalic Acid as I am not sure exactly how much to addm how to remove it from the pool after the stains are removed, what else I need to add, to run the filter or not, pH levelsm etc etc.

I think from what I have read on the net that this might be the steps required but need confirmation please.

1. Lower Chlorine levels to 0ppm
2. Raise pH to 6.8
3. Add 0.95Kg of Oxalic Acid for 75000 Liters of water.
4. Pour the acid in around the edges of the pool
5. Switch filter to circulation and leave to run for a few hours
6. When stains are removed add a additive to remove the metal compounds from the water
7. Increase the pH to 7.2 using what we call here "pH+" or "pH plus" (I have an automatic pH doser to do this)
8. Increase the chlorine level back to 1-3ppm
9. Check chlorine and pH daily and adjust as necessary
10. Keep the pH around 7.2 for 2 weeks then increase back to 7.3 - 7.4

How am i doing, does this sound about right or have I missed anything?

Would appreciate any help. Oh, if you mention any products etc by name etc can you specify what they actually do and are used for as the terms and names you use in the US do not really match up to here in France and the UK.

Thank for the help, looking forward to the replies.

Rob.
 

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You have done your homework! There are only a couple of minor changes I would make. Before you start, add a startup does of a polquat based algaecide to the pool. Wait a day between step 6 and step 7. You should also be aware that step 8 may take a while. Add the chlorine slowly and expect it to vanish for a while before the FC level starts to behave normally.

There is a completely different approach that you might want to consider. Since your stains are not on the bulk of the pool, you can put the oxalic acid in a sock or wrapped up kitchen towel and apply it directly to the stained areas without doing the whole procedure you described. This is basically the same idea as using Vitamin C tablets, just on a larger scale. This is more tedious in a way, because you need to move the sock/towel around slowly so it sits in each spot for long enough to work, which is likely to take hours of regular attention. But it saves you the whole multi-step mutli-day procedure during which you can't swim.

One final thing to keep in mind. Take care when handling oxalic acid. While it isn't wildly dangerous, it isn't something you want to get on your skin or in your eyes.
 
Ok, I'm still waiting for the chlorine levels to drop in the pool.

As i mentioned previously, I shocked the pool with the recommended amount more than a week ago and the readings i was taking showed 10ppm after shocking the pool.

It's now a week later and the level is still 6.5ppm..... this seems to be taking a very long time for the chloine levels to drop. Any advice as to why this may be? One day I tested the pool and the level dropped off to 8.5ppm, I retested a few hours later and the level was back to 10ppm. I have no idea what is going on here, I assumed with the pool uncovered, the sun on it that the levels would drop quickly, but this does not seem to be the case.

I know that sodium thiosulfate can be used to lower the Chlorine levels or "After Shock", but I cannot find any products here in France that are are designed for this and have read that using sodium thiosulfate can turn the water a greenish colour. Any suggestions would be welcomed.

I have recieved the 3 kg of the Oxalic Acid I ordered and have used about a 1kg of it to clean the steps and some areas of the pool, plus just added the reset to see what would happen. It removed a small amount of the stains but I'm guessing it reacted with the chlorine and became inactive very quickly due to the high chlorine levels.... the steps do look very clean though, so was worth it.

12 hours after adding the OA the pool has gone from cystal clear water to a murky/cloudy state... kind of white cloudy. I was reading another post, and i think it was JasonLion that mentioned the following: "Oxalic acid can also cause problems with cloudy water (it can cause calcium to precipitate as an exceedingly fine powder)."

Can I assume that the cloudy/white water is most probably due to suspended calcium in the pool? Will the sand filter remove this once moved from circulate back to filter or do i need to do something else once I have finally got the chlorine levels down and the stains removed with the Oxalic Acid?
 
Sand filters can't always get calcium particles, it depends on how large they are. Often calcium precipitates as extremely fine particles that the filter can't catch, but sometimes they clump and the filter can catch them. The calcium will go away after a while, redissolving if nothing else, if your chemical levels are appropriate.

Most likely your FC level is falling very slowly because you have a very high CYA level. However, based on some of your comments, it is possible that some kind of testing error is going on. Sodium thiosulfate is reasonably safe to use, if you can find it.
 
I had the exact problem with one of my pools last year. Pool had horrible iron stains so i actually used a product sold at home depot called IRON OUT. IT worked but the water got extremely cloudy. I believe it was the calcium coming out of suspension. AFter 3 days of running the filter (cartridge) it still hadnt cleared. The homeowners were getting worried, so i flocked the pool, vacuumed to waste the following morning and all was good.
 
thanks for the replies.

still trying to resolve this issue. the chlorine is now down to 0, after changing about 10-15% of the water for fresh. After the water change the chlorine started to fall rapidly.

Ok, so this morning the pool tested 0ppm for chlorine, pH was at 6.8 so I added 1kg of the Oxalic Acid around the edge of the pool, fired up the pump on circulate rather than filter and waited for the "magic" to happen.

unfortunately all that happened was that the pool turned completely white again (can't even see the bottom drain now) but the brown stains on the liner, some of the white PVC fittings that I hadn't cleaned manually and the bits that were left on the steps still remain.

So, i'm slightly confused now! Any suggestions? I have 1kg of the Oxalic Acide left, and at 15 Euros a KG plus delivery I'm not wanting to waste it.

Am I doing something wrong here? The OA worked perfectly on the steps when I just sprinkled a handfull in by hand to test, and that was when the pH was normal and the chlorine was up at nearly 10ppm. I had visions of adding the OA to the pool and watching the brown liner and fittings turn back to their original colour in front of my eyes.... was I hoping for to much here?

any suggestions please... Wait, pray, hope, new pool :? I have thought about the sock method but to clean 95m2 of liner and the fittings sounds like it will take forever and I'm guessing the 1Kg of OA will dissolve fiarly rapidly and I wont have enough to do the whole pool.
 
Just read your post, so I may be too late for this time

Sodium Thiosulfate, is also known as Thio-Trine, and as Hypo (used in photography prior to digital coming along) a photo supply store/house/or wedding photography shop should carry some; 1oz neutralizes 1 ppm of chlorine in a 10,000 gal pool. I have used it on many occasions in the past when doing the iron thing and then draining, once when not draining. On no occassion did I have any coloration issue. It might have been latent algae causing this issue - only guessing. It does put a tiny, nay neglligible, amount of Sulfur in the pool about 1.4 ppm per 1 oz of Thio-Trine (Sodium Thiosulphate).

One other way to reduce chlorine is to add about 28 oz of "Algaecide 60" for 5 ppm Cl in a 10,000 gallon pool to reduce the chlorine to zero and has the added benefit of protecting your pool while cleaning. Your pool is approximately 20,000 gallons.

One other hint would be to give a your pool a Mustard Shock treatment prior to doing the iron thing. This insures no algae will be there when you restart, then add either Thiosulfate or "Algaecide 60" to get to zero FC.

Once you have treated the pool if you do use Oxalic acid you will need about 50 to 60 ppm of chlorine before it stabilizes and hold the chlorine assuming 1 3/4 lbs in a 10,000 gallon pool, less if you are using only 1 lb. DO NOT pour the chlorine in all at once, bring it up to safe level based on your CYA and check hourly adding as necessary (yes you have to do it hourly for the first 5 hours then at the very least every 2 hours afterwards - takes about 12 hours), also checking the ph is around 7.2 (lower is ok for the first day or so). Keep it at 7.2 for the first week or two weeks. Note adding the above amount of chlorine in my 10,000 gallon pool reduced the CYA from 40 to 30 in the first 24 hours.

Hope this helps in the future.

Is France still as great to "live in" as I remember it 30+ years ago?
 
As concerns your issue, if I understand you correctly that the OA did not completely remove the iron stains and the pool is cloudy. And you want to clean the whole pool without moving a sock around, I hope this is correct. If you like moving socks around your 20,000 gallon pool during your next French vacation, 4 weeks I believe - seems like enough time, please read no further.

One of your main issues is that you should have used a minimum of 2 to 4 times as much OA as you did as it is less efficient a cleaner than AA.

The following is the method I have used successfully, it deviates a little from the recommended method:

1. Once the Ascorbic Acid (1-2 lbs per 10,000 gals, 2 lbs to 4 lbs for your pool) (I tried Oxalic with poor results - 4 to 8 lbs needed for your pool) is added to the pool I leave the pump on re-circulate for 3 to 4 hours.

2. Then add Jack's Purple Stuff.

3. Then turn it to filter for an additional 8 to 9 hours, in 10,000 galllon pool (preferably overnight to avoid high UV rays from the sun in Honolulu (If 20,000 gallons then 20 to 21 hours, etc.).

4. Then backwash.

5. Then vacuum the pool to waste.

6. Maybe back wash one more time 24 hours later.

If however the pool is not clean (as white in a white plaster pool) after "1. Once the acid is added to the pool I leave the pump on re-circulate for 3 to 4 hours, "Then I would forget doing "2. Then add Jack's Purple Stuff." but still do 3, 4 and 5. And go back and add more OA, in other words you had so much iron in the pool that it got used up and you need to add more, 4 to 8 lbs of OA should be able to clean any iron issue in 20,000 gallon pool, but in my personal experience it did not work, the Oxalic acid that is.

If the pool is still not clean after doing the OA twice (as in white in a white plaster pool). Then it is most probably not iron that is the issue, to test if this is the case put a vitamin C tablet on a stained area and see if that works if it does work then your OA is the problem. 4 to 8 lbs of OA should easily clean a 20,000 gallon pool, or your OA may not be too pure (also OA can take a longggg time to do its job; note 2 - 4 lbs of Ascobic acid would work better and faster (usually brilliantly clean in under 1 hour) in my personal experience.

If the pool is merely cloudy then a floc is most probably an alternative or backwashing when your gauge reads that your filter is becoming blocked, and then filter again and again until it is clear. You should also add chlorine to it's appropriate CYA normal level so as to avoid an algae breakout, yes I know you will be flushing chlorine with the cloudy backwashed down the drain but better that than an algae breakout.

Easiest and Best - In my opinion: If it is possible to completely drain you pool that would most probably be the easiest way to handle the cloudy only issue, assuming that the pool is clean but merely cloudy and that draining it will not cause any cracks or tears in the pool due to a high groundwater table, or pump out a quarter of the pool water, then refill and keep doing this until clear. If you cannot drain or do not want to drain and backwashing takes too long then I think I would floc if it were me.

You can get pure 100% AA at a health food store by buying "Unbuffered" Vitamin C powder used in cooking or at a food/catering industry supply house often for less than you can from a chemistry store, important do not buy "Buffered" it will not work.

Or buy 2- 4 lbs of small or tiny "Unbuffered" Vitamin C Tablets at a superstore, hopefully on sale, and grind then to a fine powder in a food processor.

Very Important: Do not put AA in a pool that has a pH lower than 7.2 as you could damage your pump.

Note Well: If you are not doing a complete drain you have to use a good sequestrant such as "Jack' Magic" or "Pro Team's" product otherwise the iron will simply fall out of solution and you will have the same issue in a month or so. It is a good idea to use a good sequestrant after you refill, and a a maintenance dose weekly. Also keep the pH at the highest 7.4 on an ongoing basis, some say 7.5, but my personal experience says 7.4. It is always best to drain, if you can, as this removes 99.9% of the iron, so long as your fill water is relatively iron free. If you have a pool cover put that in the pool at the same time you are using your acid to clean as that surface to has a lot of iron on it, or alternativly hang upside in the pool slowly moving a sock around it.

Good Sequestrants: ProTeam's Metal Magic and Jack's Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) or anything that contains HEDP and/or Phosphonic Acid (NOT PHOSPHOROUS)

Hope this helps.

"Vive Les Chaussettes"
 

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smallpooldad, thanks for posting your very through suggestions. I have a couple of comments on them. Draining the pool is almost never a good idea. Nothing in this case suggests that draining will be needed. Letting the PH go below 7.2 for a few days is normally just fine and is sometimes required during an AA/oxalic acid treatment. I don't think that floc is ever worth the money/effort. In particular some clouding when doing an AA/oxalic acid treatment is completely normal and generally clears up in a couple of days.


robertwo, it is no doubt too late to help you out, but it sounds like you just needed more oxalic acid and more time for the reaction to occur. Getting the FC level down to zero, or very close, at the start is important. Any FC remaining mutually destroys oxalic acid, reducing the amount you have effectively added. Also, the lifting of the stains can go very quickly or it can take several hours. In any case, it would be great to hear an update of how things turned out.
 
Update:

Finally the stains are gone.

I just added another 1kg of the OA and it cleaned up like new.

Comment on my experience:

1. As for the cloudy water, it disolves quick in a coupe or so days, or I just floced the pool left the robot running over night and the pool was fairly clear by morning.

2. As for quantity of OA, from my experience I would recommend 0.03 Gramms per liter or 0.11 Grammes per US Gallon or water.

3. Make sure that chlorine levels are 0 or very very close.

4. If the chlorine will not drop, for instance as mine did staying at 10ppm for over a week, then change 10-15% of the water for fresh tap water and it seems to kick start something and the chlorine starts to drop. i have no idea why, maybe someone can explain. I thought I read that it might be something to do with high levels of an acid that they use to stabilise the chlorine against UV. Maybe i am wrong.

5. Around the fittings that are close tot he surface, lights, jets, skimmers etc. I added a few grammes of OA directly in front of each of them and they cleaned up very very quickly. I did this about an hour or two after adding the 2kg of OA to the pool. I also added a handful or two to a sock and left this sitting on the bottom drain, just to make sure it was clean, inside and out.

Not much else to say really. Took a bit of trial and error but the end result is a clean pool looking like new.

As a final bit of education, can someone explain the principles behind testing and adjusting the alkalinity. In FRance no one has ever mentioned it and all the test kits I have seen, except one only test for chorine and pH. Why is it important, why and how to adjust it?

The same goes for shock chlorine. why use it, what does it do apart from killing algae and sterilizing the pool like normal chlorine. I thougt I read somewhere it breaks up some byproduct of chlorine, chloram....something!?!? and helps to keep a stable FC level. Is this correct?

I have attached a couple of after photos to show the brown stains have finally vanished. Not the clearest photos but the pool is still slightly cloudy.

So as a final "Task List" for anyone needing to now how to use OA, here's my list with a few adjustments from my original list based on advice given earlier in this post and my experience.

1. Lower Chlorine levels to 0ppm
2. Raise pH to 6.8
3. Add a algacide to the pool to prevent algae growing while pH is at 0
(Steps 1-3 may take a few days. Or use sodium thiosulfate to neutralize the chlorine)
4. Shut the pump off on the pool, when the levels are correct, for 2-3 hours to stop water movement before step 5.
5. Add about 28-30 Grams of Oxalic Acid for ever 1000 Liters of water
6. Pour the acid in around the edges of the pool
7. Wait 1-2 hours
8. If fittings such as the jets, lights, skimmers etc are very stained you can add a few grams of OA directly in front of the fitting. This can help to quickly remove the stains and allows the OA to penetrate inside the fitting such as jets and skimmers. This step is not really necessary but is there if you want to be sure the stains are gone on the PVC fittings.
9. Switch filter to circulate and restart.
10. Expect the pool water to turn cloudy white.
11. Wait 24 hours with the pump running in circulate mode (Not filter!)
12. If the water is very cloudy and you can't tell if all the stains are removed, either switch the pump/filter back to Filter mode and leave the pump and filter running for a couple of days until the pool clears or backwash the filter, floc the pool and run the filter overnight. The pool should nearly clear my morning.
(At this point, if the stains have not been removed, they either are not going to be removed by the OA or you need to add more. To test if the Oa is actually going to work on any stains that have not been removed, take a white sock, fill it with a couple of handfuls (use gloves) of OA, tie it closed and place it over one of the remaining stains. If the stain is removed (could take 1-20 minutes) then add more OA, maybe half the original amount again. If it isn;t removed, look for alternatives as it is unlikely the OA will remove the stains)
13. When the stains are removed backwash the filter, switch back to filter mode and add a sequestrant as per manufactures directions to remove the metal compounds from the water
14. Wait 24 hours
15. Start to increase the pH to 7.2
16. Increase the chlorine level back to 1-3ppm. Add the chlorine slowly and expect it to vanish for a while before the FC level starts to behave normally.
17. Check chlorine and pH once or twice a day and adjust as necessary
18. Keep the pH around 7.2 for 2 weeks then increase back to 7.3 - 7.4
19. Add followup doses of the sequestrant as per the manufactureres instructions to be sure the stains do not return.

I hope that helps anyone in the future looking for a detailed list on how to use OA for iron stained pools. Good luck and thank you to all who helped me out.
 

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robertwo said:
As a final bit of education, can someone explain the principles behind testing and adjusting the alkalinity. In FRance no one has ever mentioned it and all the test kits I have seen, except one only test for chorine and pH. Why is it important, why and how to adjust it?

The same goes for shock chlorine. why use it, what does it do apart from killing algae and sterilizing the pool like normal chlorine. I thougt I read somewhere it breaks up some byproduct of chlorine, chloram....something!?!? and helps to keep a stable FC level. Is this correct?
Click to expand...
Total Alkalinity (TA) is mostly a measure of bicarbonate in the water. This acts as a pH buffer so has the pH move less when acids or bases are added to the water. However, TA is also a SOURCE of rising pH since some of the carbonates in the water are in the form of carbon dioxide that outgasses from the pool. Essentially, pools are intentionally over-carbonated, but when the carbon dioxide leaves the pool it raises the pH (with no change in TA for technical reasons I won't get into here).

The carbonates are also important to saturate the water with calcium carbonate to protect plaster surfaces which is why TA is one component in the saturation index you can calculate using The Pool Calculator. Since your pool is vinyl and assuming you have no grout in tile exposed to the pool water, then the saturation index need not be near zero so you don't have to have Calcium Hardness (CH) and other parameters including TA adjusted. In your pool, the appropriate TA level would be one that is low enough where you find the pH is stable, assuming you are using chlorinating liquid or bleach (or even Cal-Hypo) as your source of chlorine. Usually this is around 80 ppm, but might be 60 or 70 ppm for your pool.

If your TA is high and you find that the rate of pH rise in your pool is fairly rapid, then you can lower the TA by following the Lower Total Alkalinity procedure. This just accelerates a process that would occur over time anyway since not lowering the TA would have you add acid every so often to lower the pH and that would slowly lower the TA. The TA lowering process makes this go faster by having the pH be lower and aerating the water. Once the TA is lower, the pH should be more stable.

There is no such thing as shock chlorine in spite of manufacturers labeling some of their chlorine as "shock". It is identical chlorine as other sources and is usually Dichlor or Cal-Hypo or sometimes powdered Trichlor. The best chlorine to use to shock a pool to use is chlorinating liquid or 6% unscented bleach as it does not increase CYA or CH. A properly maintained pool with a Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level (see the Chlorine / CYA Chart) does not need regular shocking. Disinfection, algae prevention, oxidation of bather waste, and elimination of chloramines is something that happens continuously in a properly managed pool and there is no need for shocking unless there is an unusual event such as a fecal accident, dead animal, unusually high bather or organic load, etc.

As for the metals in your water, realize that the oxalic acid (or ascorbic acid which would also work) just reduces the iron into a form that is better held by a metal sequestrant and that the metal sequestrant holds onto the iron so that it will not stain. The iron is not actually removed from the water except by water replacement. So you need to maintain a sequestrant level to keep the metal from staining and should also be careful not to let the pH or chlorine levels get too high as well. Depending on the sequestrant you are using, you may find that your chlorine demand is higher than before because the chlorine will break down the sequestrant over time (HEDP is more resistant against breakdown from chlorine).

Richard
 
thanks for the reply Richard, very informative and helpful.

A quick question about TA and pH. Most people I speak to say their pool tends to drift from the 7.3 range upwards, thus becoming more alakaline with a pH moving towards 8. My pool goes completely the opposite way, drifting from 7.3 to 6 and over the winter as we had the pH regulator set to dose acid and not alkaline the pH must have kept moving to become more acidic. When I checked the pool around the begining of spring, maybe 6 months after it had last been used the pH was off the scale of any test kit I had and the pH regulator was reading 4.3.

I recalibrated the pH probe and there was no change. I checked it after calibration using pH 7, 4 and 0 solutions and it indicted the correct levels every time, so I ruled out a fault with the pH regulator.

It took a lot of PH+ to correct it. I have now changed the pH regulator to dose alkaline instead of the acid.

Do pools usually become more acidic or alkaline, or does it just depend on location, chemistry, external influences?

Actually it just occured to me while writting this, could there be a problem with the Peristaltic Pump? Is there anyway that the acid could have been syphoned from the holding tank through the pump and in to the pool by way of the high flow rate of pumped pool water causing a vacum and basically sucking the acid out of the tank? I wonder if the pumps have any adjustment to stop this? Maybe increasing the wheel pressure on the rubber tubing in the pump......
 
Most pools around here tend to have their PH drift up because of CO2 outgassing, which raises the PH. Pools that use trichlor, which most people use, just not the people around here, tend to have PH drift down because trichlor is acidic. Every now and then you run into a pool that goes the opposite way than you would expect, but that is rare.

It is very unusual for a peristaltic pump to allow syphoning. The wheels in the pump should completely seal the tubing, preventing that from happening.
 
robertwo said:
Update:

Finally the stains are gone.

I just added another 1kg of the OA and it cleaned up like new.

Comment on my experience:

1. As for the cloudy water, it disolves quick in a coupe or so days, or I just floced the pool left the robot running over night and the pool was fairly clear by morning.

2. As for quantity of OA, from my experience I would recommend 0.03 Gramms per liter or 0.11 Grammes per US Gallon or water.

3. Make sure that chlorine levels are 0 or very very close.

4. If the chlorine will not drop, for instance as mine did staying at 10ppm for over a week, then change 10-15% of the water for fresh tap water and it seems to kick start something and the chlorine starts to drop. i have no idea why, maybe someone can explain. I thought I read that it might be something to do with high levels of an acid that they use to stabilise the chlorine against UV. Maybe i am wrong.

5. Around the fittings that are close tot he surface, lights, jets, skimmers etc. I added a few grammes of OA directly in front of each of them and they cleaned up very very quickly. I did this about an hour or two after adding the 2kg of OA to the pool. I also added a handful or two to a sock and left this sitting on the bottom drain, just to make sure it was clean, inside and out.

Not much else to say really. Took a bit of trial and error but the end result is a clean pool looking like new.

As a final bit of education, can someone explain the principles behind testing and adjusting the alkalinity. In FRance no one has ever mentioned it and all the test kits I have seen, except one only test for chorine and pH. Why is it important, why and how to adjust it?

The same goes for shock chlorine. why use it, what does it do apart from killing algae and sterilizing the pool like normal chlorine. I thougt I read somewhere it breaks up some byproduct of chlorine, chloram....something!?!? and helps to keep a stable FC level. Is this correct?

I have attached a couple of after photos to show the brown stains have finally vanished. Not the clearest photos but the pool is still slightly cloudy.

So as a final "Task List" for anyone needing to now how to use OA, here's my list with a few adjustments from my original list based on advice given earlier in this post and my experience.

1. Lower Chlorine levels to 0ppm
2. Raise pH to 6.8
3. Add a algacide to the pool to prevent algae growing while pH is at 0
(Steps 1-3 may take a few days. Or use sodium thiosulfate to neutralize the chlorine)
4. Shut the pump off on the pool, when the levels are correct, for 2-3 hours to stop water movement before step 5.
5. Add about 28-30 Grams of Oxalic Acid for ever 1000 Liters of water
6. Pour the acid in around the edges of the pool
7. Wait 1-2 hours
8. If fittings such as the jets, lights, skimmers etc are very stained you can add a few grams of OA directly in front of the fitting. This can help to quickly remove the stains and allows the OA to penetrate inside the fitting such as jets and skimmers. This step is not really necessary but is there if you want to be sure the stains are gone on the PVC fittings.
9. Switch filter to circulate and restart.
10. Expect the pool water to turn cloudy white.
11. Wait 24 hours with the pump running in circulate mode (Not filter!)
12. If the water is very cloudy and you can't tell if all the stains are removed, either switch the pump/filter back to Filter mode and leave the pump and filter running for a couple of days until the pool clears or backwash the filter, floc the pool and run the filter overnight. The pool should nearly clear my morning.
(At this point, if the stains have not been removed, they either are not going to be removed by the OA or you need to add more. To test if the Oa is actually going to work on any stains that have not been removed, take a white sock, fill it with a couple of handfuls (use gloves) of OA, tie it closed and place it over one of the remaining stains. If the stain is removed (could take 1-20 minutes) then add more OA, maybe half the original amount again. If it isn;t removed, look for alternatives as it is unlikely the OA will remove the stains)
13. When the stains are removed backwash the filter, switch back to filter mode and add a sequestrant as per manufactures directions to remove the metal compounds from the water
14. Wait 24 hours
15. Start to increase the pH to 7.2
16. Increase the chlorine level back to 1-3ppm. Add the chlorine slowly and expect it to vanish for a while before the FC level starts to behave normally.
17. Check chlorine and pH once or twice a day and adjust as necessary
18. Keep the pH around 7.2 for 2 weeks then increase back to 7.3 - 7.4
19. Add followup doses of the sequestrant as per the manufactureres instructions to be sure the stains do not return.

I hope that helps anyone in the future looking for a detailed list on how to use OA for iron stained pools. Good luck and thank you to all who helped me out.
Click to expand...
Hi Roberttwo. Thank you for asking the question that started this thread. I have a rust stained concrete pool and had a hard time finding out that Oxalic acid was the magic powder I needed. All is well now but I just wanted to thank you for sharing. Very generous of you.
 
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