Used Hydrogen Peroxide for Removing Metal Stains - Results

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for the reply. I changed the log to base 10, and as I am sure you know if you created that simple spreadsheet the phosphate numbers would have to exceed 117,000,000
ppb to create an issue; even I did not exceed that high number with a number slightly in excess of 65,000 ppb or 0.06% of that high figure.

I then did a little more research on the web and calling Dow, the "Stability Index" is based on the "Stiff & Davis Stability Index" used for high salinity situations based on TDS in excess of 10,000 mg/L, or if you like the index is used primarily in the desalination of high-salinity brackish waters and seawater desalination, obviously not appropriate to freshwater and saltwater swimming pools with a low TDS measurement.

So this equation will not work for us.

Dow Paper is here:

http://msdssearch.dow.com/Published...5.pdf?filepath=/609-02017.pdf&fromPage=GetDoc

I wished I had "Googled" a bit more before I posted that paper, but learning from mistakes can have its benefits. It seems that maybe the 11.755 number has something to do with "Temperature coefficients for pH in seawater" the numbers seem close to these numbers mentioned in this paper on page 681, here:

http://www.aslo.org/lo/toc/vol_14/issue_5/0679.pdf

As to the the 0.65 number in the original paper I linked to, here:

http://msdssearch.dow.com/Published...b8.pdf?filepath=/609-02023.pdf&fromPage=GetDo

I do not know how that relates in the formula but I will ask Dow Chemical, they have been very fast at getting back to me. So I will ask them how these numbers were derived and can they be altered in a low TDS, non-seawater situation. My guess would be not very likely, but we will see.

Fortunately for me they treat me, as do you, as an inquisitive child and again, like you, they let me follow my hunches without blowing me out of the water and damping my enthusiasm to get to the bottom of this issue.

What I have learnt so far while both "Experimenting" and "Googling":

1. Orthophosphates can create scaling issues in sufficient quantities see this article on boilers (reading on beyond page 72 is also very interesting:

http://books.google.com/books?id=pN...&q=Calcium Phosphate Scale Prevention&f=false

It seems that any where from 10 to 40 ppm, or 10,000 to 40,000 ppb might/can/will create "Calcium Phosphate Scale". As boilers operate at a considerably higher temperatures than a swimming pool would not then these threshold figures of 10,000 to 40,000 ppb be lower for a swimming pool?

Also low alkalinity can create the potential for scaling but I think most persons are aware of that.

2, From "Googling" and "Personal Experience" it seems that Hydrogen Peroxide in the presence of HEDP,above an HEDP level of 13 ppm (as I lost 20+ ppm in the process it might be best to start with a level of say 40 ppm), and if the temperature is ideally 70 F or below will remove "Calcium Phosphate Scale" and possibly just plain "Calcium Scaling." It is best performed in conjunction with a pH lower than 7, I used Ascorbic Acid (around 6.6 to 6.8). In my case quite spectacularly.

3. From "Googling" and "Personal Experience", it seems that at a temperature nearing or above 77 F HP does not work as well, some articles state it will not work at all if HEDP is present above 13 ppm and temperatures exceed 77 F. I have not tried that.

4. For the HP method to work apart from the above prescribed parameters iron and/or orthophosphates must exist in sufficient quantities to create a catalyst.

5. At present nobody, it seems, has worked out what the upper limits for phosphates in a pool are before "Calcium Phosphate Scaling" will occur. Although the above paper sets the lower limit at 10,000 ppb in a boiler so maybe half that say 5,000 ppb in a cooler swimming pool. This of course is a wild guess for safety's sake.

6. I still think that when person's answer the phosphate question and are told not to worry about them so long as chlorine and CyA are kept in check that this is wrong headed. One must tell them how to properly know their phosphate level by proper dilution and go from their. I agree my pool gets a lot of wind but so do some other pools and even though my level was for most of the 1 1/2 years was kept at a sequestrant level, using HEDP at 10 ppm, the phosphates rose to over 65,000+. Many persons just doing the test without dilution will assume it is 1,000 ppb or 2,500 ppb depending on the "Phosphate Test Kit" they use, and this can prove to be a serious issue as regards scaling.

7. A question. Is it conceivable the in the process when the oxygen molecule is released from the HP it remains in the pool longer as HEDP is present and helps oxidize both phosphate and iron?

I do not know if this article can bring any light to that question but here it is anyway from Columbia University:

http://www.columbia.edu/~ap2622/pdf/Stability of hydrogen peroxide in sodium carbonate.pdf

8. Since I last wrote a few days ago my HEDP level has fallen from 80 ppm to 38 ppm, why I do not know. Any ideas? The filter has seen no increase in pressure but I did add 27 oz of CyA to up the CyA level from 60 to 80 about 3 or 4 days ago. The leaf canister nylon type filter material has lightened from a light medium brown to off-white, new it is white. The "Phospate Test still reads around 1,500 ppb.

9. One interesting thing happened this morning, one of those long garden slugs had fallen into the pool overnight, unlike all previous occasions it did not leave a stain. I think this has something to do with the "Calcium Phosphate Scale" being removed.

10. Nearly forgot the HP method in the manner described above removes a lot of orthophosphates, 63.500+ ppb in my case going from 65,000+ ppb down to 1,500 ppb over 4 treatments. Agood benefit to those with high phosphates.

Still no news on Thorium Nitrate the lady at Palintest said she was upset because the UK manufacturer had not gotten back to her.

The Pool looks really good and despite the pH rising above 7.5 there was no iron separation, it is now back down to 7.3

Thank you

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

The problem with calculating the precipitation of calcium phosphate is that there isn't a single definitive solubility product that I could find. It's really all over the map. See this post I wrote a while ago that listed 5 different solubility products ranging from 1x10^-26 to 1x10^-33 which is a huge range of over 10 million in concentration. That's why I never spent time putting together any sort of calcium phosphate precipitation table. You can look at the Dow info all you want, but I'd never translate it into something definitive for a pool until the scientific community gets a better handle on the true solubility product AND on the various stability constants for relevant ion pairs since they tend to make things seem more soluble. Also, one can have different degrees of over-saturation without precipitation or scaling. These things are not so simple. Even the calcium carbonate system with its calcite saturation index is just a guideline, but fortunately is much, much better understood and has much more consistent solubility and stability constants. Nevertheless, we'e seen that in real pools we don't generally see calcium carbonate scaling until the CSI gets above +0.7 or so (though in a saltwater chlorine generator cell or in a gas heater it can be a much lower CSI in the bulk water because the pH in the cell at one plate is very high and the temperature in the gas heat exchanger is much higher) while in spas we've seen scaling at around +0.3 or so.

7. A question. Is it conceivable the in the process when the oxygen molecule is released from the HP it remains in the pool longer as HEDP is present and helps oxidize both phosphate and iron?

Oxygen is not a strong oxidizer. When hydrogen peroxide breaks down, it forms hydroxyl radicals (similar to chlorine) especially when exposed to the UV in sunlight and hydroxyl radicals are strong oxidizers. However orthophosphate does NOT get oxidized -- it's already essentially fully oxidized. Iron also will already be oxidized by chlorine. What hydrogen peroxide does that is unique is that it can be both a reducing agent and an oxidizing agent and with iron it can go both ways converting ferric to ferrous and then ferrous to ferric. The iron being a catalyst means that it does not get used up in the reaction and essentially just accelerates the breakdown of hydrogen peroxide.

Again, there is no mechanism seen for the orthophosphate removal other than precipitation of it and we know that calcium phosphate will precipitate if both levels are sufficiently high. However, you have apparently gotten the phosphate levels down well below where it would precipitate with calcium at your levels. This paper describes how it is iron that precipitates (coagulates) with phosphate and that hydrogen peroxide can enhance this process. The hydroxyl radicals produced from hydrogen peroxide apparently aid in the process. Iron (ferric) phosphate has a solubility product of [Fe³⁺][PO₄^3-] = 1.3x10^-22 compared with calcium phosphate of [Ca²⁺]³[PO₄^3-]² = 1x10^-26 and lanthanum phosphate (the usual phosphate remover) of [La³⁺][PO₄^3-] = 3.2x10^-27. So basically it takes 10,000 times the concentration of iron to precipitate phosphate compared to lanthanum. So maybe what is happening is that you've got so much iron bound to your HEDP that it's enough to precipitate out with phosphate but that it takes hydrogen peroxide to aid in the release of the iron from HEDP and get oxidized to ferric and then precipitate with the phosphate. Of course, if this is what is happening, then I wonder why one doesn't just 1) reduce iron stains using a reducing agent and then 2) add orthophosphate to the water and 3) oxidize the iron from ferrous to ferric and precipitate iron phosphate. That is, why not use orthophosphate with hydrogen peroxide to get rid of iron as well as the much of the added orthophosphate. The thing is that based on the solubility products, the iron levels would have to be extraordinarily high for the phosphate level to be removed as much as you are seeing. This may be the case with your pool that gets extraordinary amounts of iron added to it that mostly are getting bound to the HEDP. Unfortunately, this doesn't sound like a great way of removing phosphates -- intentionally adding such high amounts of iron to do this would leave iron leftover. If one wants to remove phosphate and doesn't already have extraordinary iron amounts, then adding lanthanum chloride won't have leftover iron side effects.

If the above is true, then the good news is that perhaps using the hydrogen peroxide has not only removed a lot of phosphate from the pool, but also much of the iron that was bound to HEDP. If that is the case, then you shouldn't need as much HEDP in the pool after the treatment to prevent metal staining because there will be less iron that is bound to it. If you were really precipitating iron phosphate, it should not have been a white precipitate but been yellow-orange in color as shown in this link as opposed to the calcium phosphates that are generally white. If your iron tests measure total iron including that which is bound to HEDP, then you should see that iron level drop if iron phosphate was getting precipitated.

As for the advice given to people on this forum, you are forgetting that most people are not using metal sequestrants because most people do not have the high iron problem that you have. Also, even for those that do, we have not received any regular reports of scaling from those with high phosphates and those with high calcium have been able to manage their pools with TA and pH management (and if the phosphates were not measured correctly or at all, then having a lower TA help with the scaling means it's calcium carbonate scaling and not calcium phosphate scaling). I'm sorry to say that your situation is rather unique and that's why the general advice of not worrying about the phosphate level is still applicable to nearly all pools. Now if we hear of someone that is using large amounts of HEDP on a regular basis, then we can warn about possible calcium phosphate scaling if their calcium level isn't low.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for all the effort you put into that reply and I agree with all the points you made. It is true that Hawaii is rather unusual because of its generally strong trade winds and volcanic iron soil and dust with some manganese added.

Well as you stated nobody really knows for sure what the threshold level for phosphates are in a pool before scaling appears , due in great part, as you stated, to the offsetting chemical components such as calcium and high pH in the salt chlorine generating cell and heater (which I use infrequently). And we will not know until someone does a lot of research.

I think the leaf/slug stain issues that occurred in my pool before removing the scale with the HP method is a good "Canary in the Coal Mine" for possible build up of scale. So if someone starts to get stains in their pool all of a sudden adding HP with Ascorbic Acid at a temperature below 70 F might solve their issue if there is enough iron and/or orthophosphate in the pool. Sadly nobody really knows as you stated what that level of iron and/or orthophosphate has to be. So the HP method may or may not work. But as it is relatively inexpensive to do, it is I think worth a shot. And most certainly better than an acid wash.

For persons taking over a very neglected pool this HP Method might be of great help to remove orthophosphates and aid in the sequestering out of iron and possibly calcium scales.

In some of the articles it mentioned scaling and in particular calcium phosphate scaling acted more like a sticky substance so iron instead of being sequestered was being stuck to the scaling, so while the AA treatment might lift the the iron stain it does not get rid of the underlying problem of scaling and so returns despite HEDP being in the pool. If the scaling were removed then the iron staining issue might not re-return as frequently. I know in my pool that when I used to rub my fingers over the wall a small amount of calcium would rub off, since removing the scale no calcium rubs off on my fingers. This test might also be appropriate for scaling issues.

As regards iron phosphate I did not see that strong orange/yellow color in the dust when backwashing.. It might be correct that iron was not removed or that the the amount of calcium phospate scaling, being more white in color, overwhelmed the color in the backwash dust. Without a proper chemical analysis of the backwash dust it would be impossible to say.

I think part, possibly all, of my scaling problem was the result of trying to keep the CSI in the -10 to -30 range by keeping the calcium at in the 600 to 650 range, as I keep my pH at about 7.3 to avoid iron staining. I stopped doing this and lowered it the calcium level to 350 about a year and a half ago after I read that you all felt 350 would be better. The SWG cell now has little to no scaling when I check, about once a month.

Question:

Would upping the Alkalinity into the 100 to 120 ppm be better in order to lower the CSI into a better range, I think not, as the pH may rise too quickly, but I am simply asking a question? My alkalinity stays firm at 80 ppm with my present setup and I use very little acid, maybe lowering it from 7.4 or 7.5 to 7.3 once, sometimes twice a week.

Well apart from response on the Thorium Nitrate I think we are all done on this subject and I thank you again for your patience, guidance, time and kind help.

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

You mean raise the CSI, don't you? Raising the TA raises the CSI and you are concerned that your CSI is too low, is that correct? If it's only somewhat low, such as -0.1 or -0.2 or even -0.3 (I don't know where you are getting your -10 to -30 and presume you mean -0.1 to -0.3) then that's fine since a slightly negative CSI will help to prevent calcium carbonate scaling in the SWCG cell. The effect on good plaster should be small. Of course, one can always raise the CSI to that balance point where the SWCG doesn't get scaling but is as high as can be to get closer to 0 to minimize the risk of dissolving plaster, but that's getting picky since quality plaster won't be so sensitive to such water chemistry. And as you point out, a higher TA leads to more pH rise so generally you keep your TA low and raise your CH if you want to raise the CSI. Of course, in your situation you've got calcium phosphate to worry about -- or at least you did until you got your phosphate level down.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Yes I did intend to write "raise" to -0.10 to -0.30.

These are my present numbers (using Pool Calculator):

Cl 4
pH 7.3 (to avoid iron staining and have -0.1 pH as reserve insurance)
TA 80
CH 350
CyA 80
Salt 3200/3300
Borates 0 (or very small)
Orthophosphates around 1500 ppb
HEDP Sequestrant 38 ppm
Temp 78F (as we live up at a 1000ft with trade winds blowing over the pool our water after April rarely gets colder than 78 F until November, and rarely goes above 84 F, in winter it can go to the mid 60s)

For a CSI of -0.52

If TA was changed to 120 ppm then CSI would be -0.29.

My experience with raising the calcium to 600 in our water has not been good, SWG cell gets scale quickly but CSI is ok at -0.29.

So I will try an in between path of TA at 100 and Calcium at 425 for a CSI of -0.30.

Does that sound OK, any other suggestions would be welcome?

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

That sounds OK and you can also check on the condition of your plaster to see if the lower CSI is having any effects (mostly pitting or uneven surface deterioration). I suspect it's OK.

Another option is to use 50 ppm Borates since that should significantly cut down calcium carbonate scaling in the salt cell since it is a strong pH buffer against a rise in pH and it is the rise in pH at the hydrogen gas generation plate that causes scaling even when the CSI is negative. The borates will roughly cut down the amount of pH rise in half. Is there are reason you aren't using borates?

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for the reply. I will try the borates but first I would like to order a borate test kit, although plaster does not look like it is pitting currently.

I do have a new dog around 73 lbs but she never drinks from the pool unlike my old dog who passed away. In fact she never goes near it after she fell in the first day we got her.

I will let you know how it went sometime in the future.

Thank you.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chemgeek,

Early this morning I looked at my skimmer to see if it needed cleaning out. As I mainly use my suction side cleaner to clean the pool, unless it is windy which has not been for a few days, I look at it once or twice a week.

I keep a pool sock in the skimmer basket, as the suction side cleaner pulls most of the gallons per minute there is very little flow through the skimmer itself unless I turn off the suction cleaner which I have not done for some days. Well you were correct, the sock WAS the color you described in your link here:

http://en.wikipedia.org/wiki/Iron(III)_phosphate

A little lighter maybe but definitely that color so it seems we are sequestering iron, possibly some Iron(III) phosphate, ferric orthophosphate, or ferric phosphate. I thought you might like to know this.

I washed out the sock, the color lightened somewhat. Interestingly the suction side cleaner nylon leaf basket actually got lighter maybe because the pressure was greater and pulled the iron based phosphates to the filter, or because the mesh is nowhere near as fine.

Hope this helps.

Thank you for your time.

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

Well now this is all starting to make a lot more sense. The hydrogen peroxide reduces the iron in stains to ferrous, then re-oxidizes it back to ferric where it combines with phosphate in the water to precipitate thereby lowering both iron and phosphate concentrations. And as noted in some papers, the hydroxyl radicals from hydrogen peroxide may aid in this precipitation process. It may also be the case that the hydrogen peroxide does the same thing to the iron bound to the metal sequestrant or to iron in equilibrium with it. So one really can't use hydrogen peroxide as a way to reduce phosphates generally because one doesn't normally want to add iron to their pool, but if one already has iron in the pool then using HEDP and having increased phosphates as a result can be managed by using hydrogen peroxide to remove both. That's actually a pretty decent thing to do in a high iron situation such as yours.

Thanks for keeping us posted.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for the reply.

Well it is good to know that the "Hydrogen Peroxide (HP) Method" in conjunction with the Ascorbic Acid (AA) Method, at a temperature of ideally lower than 70 F and no higher than 78 F, will work to significantly reduce the ppm(s) of iron and the ppb(s) of orthophosphates if there are enough parts per million (ppm) of iron and (ppb) of orthophosphates in the pool, if one is using and HEDP sequestrant. 40 ppm seems to be a good number for the HEDP sequestrant as one can lose approximately 20+ ppm when the combined method is used, and there needs to be more than 13 ppm for it to continue working.

So it seems that this would work for persons with iron and orthophosphates if one has been using an HEDP sequestrant for some time, say 9 months or more, sufficient ppm might be present in the pool.

However if there are insufficient quantities of iron present might the addition of Aluminum Oxide, or another non-staining oxide, work as a catalyst to remove orthophosphates? Might Aluminum Oxide stain, or scale, the pool and what quantity would be needed for 10,000 gallons.

The following links discuss this:

http://www.lenntech.com/periodic/water/aluminium/aluminum-and-water.htm

http://eps.mcgill.ca/~courses/c590/LijklemaES&T(14)1980_adsorption_Fe&Al_oxides.pdf

Aluminum Oxide health issues:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2782734/

Thank you.

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

It's not iron as a catalyst to hydrogen peroxide breakdown that is what removes phosphate, but rather that ferric iron precipitates with phosphate because of its low solubility product. Unfortunately, aluminum phosphate has a much higher solubility product K_SP of 9.84x10^-21 so aluminum cannot be used to reduce phosphate unless you use rather high aluminum concentrations (which is what is sometimes done in water treatment). This is why lanthanum is used to remove phosphate via precipitation because lanthanum phosphate is rather insoluble so it doesn't take very much lanthanum to accomplish the task with it's K_SP of 3.2x10^-27. You'd have to use about 3 million times as much aluminum as lanthanum to precipitate down to the same resulting level of phosphate.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for the reply.

Would then using less lanthanum, very expensive here in Honolulu, with Hydrogen peroxide remove the same amount as using more lanthanum?

Thank you.

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

The hydrogen peroxide just gets the iron out of the stains and possibly the HEDP so that it can then precipitate with the lanthanum. It will not reduce the amount of lanthanum that is needed. The amount of lanthanum needed is a function of the amount of phosphate so yes, that gets very expensive in a pool with high phosphates. So you'd want to reduce it first with the iron as you have done, but quite frankly there's not much point in trying to lower it much further since you are just adding more with the HEDP. Instead, you should be able to get to a steady-state level of iron and phosphate. As more iron gets blown in and gets sequestered by HEDP, then as that builds up and the phosphate level builds up from HEDP breaking down, you can do a hydrogen peroxide treatment and precipitate more iron and phosphate. In theory, you should be able to use a somewhat lower level of HEDP than you were using before because you will be physically removing iron from your pool.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

Thank you for the reply and apologies for my late response.

I agree with your idea of waiting. It will also be interesting to see how long it now takes for iron stains to come back, hopefully a long time but we will see.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

As promised I would reply on Thorium Nitrate 0.1% sequestrant test liquid. "Palintest" has still not replied but LaMotte on their website states it is good for 2 years not one.

Also an update, the sequestrant level is now at 18 ppm down from 60 ppm in just a couple of weeks. Backwashed the pool and the color you described here:

http://en.wikipedia.org/wiki/Iron(III)_phosphate

Was present again, albeit quite light. There was little dust but interestingly quite a lot of large granules, . The pool is looking very good and seems to get lighter daily.

As Jack's Magic states the sequestrant, "The Purple Stuff," can be maintained at two 32 oz bottles in a pool with a heavier iron load I think I will do that. This equates to about 42 ppm of sequestrant.

Thank you.

 

[smallpooldad]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

chem geek,

In my never ending search for the perfect pool I did one more (last for many months I hope) "Hydrogen Peroxide and Ascorbic Acid Treatment", using 11 bottles of CVS's 32 oz 3% Hydrogen Peroxide (352 oz) put in as darkness fell, and 1 lb of Ascorbic Acid 2 hours later. Adding back 3 Large Jugs of Walmart Bleach (Chlorine) at 5 am the following morning before sunrise, and on the following day (2 days later) at 7:00 am one 76 oz box of Borax to raise pH back to 7.1 ppm.

The pool numbers prior to the treatment were:

Cl 6
pH 7.3
TA 80
CH 325
CyA 80
Salt 3200
Borates 6
Orthophosphates 2000 (ppb)
Jack's Magic Sequestrant (HEDP) 42 ppm
Temp 78F (late correction this should read 75F)

The results:

The filter once again became blocked by 5 am the morning following the overnight treatment. The backwash indicated the same off yellow color of ferric orthophosphate staining I saw before.

But the few areas that still had very very light calcium (probably Calcium Phosphate staining/scale) had gone, gone, gone. The pool looks as good as I think it ever will at its age 16+ years, so I am done. I backwashed again in the evening after running the suction cleaner half the day and the skimmer the other half (there was a lot of muck to skim), and again the same color.

It seems that during this final process no orthophosphates were removed, as you speculated, the initial 2000 ppb were still present after this treatment when tested. The HEDP sequestrant dropped from 42 to 38 ppm, so quite minimal this time.

But it seems that once the Hydrogen Peroxide had removed all it could of the Calcium Phosphate staining/scale, or possibly ferric orthophosphate, or a combination of both it went for something else.

The CyA dropped from 80 ppm to 50 ppm, I have tested this number 5 times to make sure I was correct. In fact the chlorine level was dropping so fast I had to up the SWG level significantly to keep up. Today I am adding back 30 ppm CyA to get back to 80 ppm.

I think/guessing then that the process of mostly removing scale is complete when the HP starts to eat significant quantities of CyA.

A number of Greek philosophers, indicated in their writings that one cannot pronounce the statement as true unless it can be supported by logic or empirical evidence. Well I think at least I have some well documented evidence of what occurred.

As I stated before I think, as was probably the case with my pool, the real problem was a slow build up of scale over many years, the iron merely highlighting the problem. As scale is tacky by nature it does not allow all of the iron to be dissolved back by the HEDP sequestrant. The AA treatment does render the pool significantly less brown but the underlying problem of scale, if not removed, allows the staining to come back more quickly than would otherwise be the case. Removing the scale should help to keep the pool stain free for much longer. But only time will tell and prove the evidence of that statement. I will report back with an update in 6 months.

It is possible that many persons posting to this site of the presence of iron staining appearing after 4 to 6 years of a stain free pool are observing a combination of scale and a little iron, and not full blown iron issues. Certainly the "Hydrogen Peroxide and Ascorbic Acid Treatment" is significantly less troublesome and dangerous than doing an "Acid Wash", or at the very least, worth giving a try.

Thank you for your time. And Yes I am really done with this for the moment.

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

Thanks for the update. It does appear that a combination of ascorbic acid and hydrogen peroxide treatments seems more effective at removing iron staining, especially if associated with calcium carbonate scale.

As for CYA, we know that chlorine slowly oxidizes it, but to know if hydrogen peroxide does that faster we should do a controlled experiment without the other stuff in the pool. Perhaps hydrogen peroxide breaking down in sunlight creates more hydroxyl radicals and perhaps these attack CYA. Chlorine breaks down to produce hydroxyl radicals as well so I'm not sure what makes hydrogen peroxide so special in this case unless there's some intermediate associated with hydrogen peroxide that is involved in oxidizing CYA. It is also possible that the CYA isn't getting oxidized, but getting removed in some other way such as precipitation though that seems less likely.

 

[Swampwoman]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

Hi guys. I've attempted to more or less follow this thread, but allow me to craft the "Experiment for Dummies" version for an imminent trial by yours truly. While I accept full responsibility for my results, Richard, please let me know if you think there may be unintended consequences

Situation: I have a 22,000 gallon vinyl pool with known iron from well water and a jack's magic habit that has netted about 25,000 orthophosphate.

Experiment (if I've read correctly):

1. ive already added polyquat 60 for extra insurance
2. 2 - 32 oz containers of jack's pink are en route to sequester

3. At nightfall, with ph at 7.2 add 1 ppm, or in my case, 2.2 gallons of 27% hydrogen peroxide, aka SoftSwim C ( or 35% if I can find it)
( have I got that part right?)

4. Consider adding in 2 lb Ascorbic acid (have same on hand...would it be better to test straight hp or combine?)

5. Expect to need to backwash by a.m.

6. Expect it is possible to need to add stabilizer if some of my CYA oxidizes, so check

7. Expect it to take extra chlorine to replace that reduced by hp, and even more if I use AA.

8. Should I expect ph adjustment necessary? I was unclear on this.

Thanks in advance for any input. Have a grad party this weekend so won't be undertaking til the following weekend, but need to get stocked up.

Thanks and cheers,
Swampwoman

 

[RisLC]

Hydrogen Peroxide for Removing Metal Stains

I was reading the posts regarding hydrogen peroxide for removing metal stains, and it is very interesting. But, how do you determine how much hydrogen peroxide to use?

 

[chem geek]

Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul

Your list looks correct. As for ascorbic acid, that depends on whether or not you've got additional metal stains you want removed. If instead you are doing this procedure to see if the metal bound to the sequestrant along with the orthophosphate in the water can be mutually precipitated to lower both concentrations, then the ascorbic acid should not be necessary. As for pH adjustment (after the initial lowering), I don't think it will be necessary.