Solution for iron problem

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
TheMartin

Solution for iron problem

Postby TheMartin » Fri 27 Jan, 2012 17:10

Hello Everybody!!

Because brown water caused by excessive iron in water drove me crazy until now, I want to share the 2 possible definite solutions with this community, hoping they make this post a sticky :wave: :

1- The first method is getting the iron out of the water. This is done by raising the pH level to above 8.2 (this is usually achieved with 2 lbs. of sodium hydroxide for every 8000 gallons of water). Then you have to add pool-magnet (chelating agent - follow label instructions) and let the water recirculate for half an hour and then let all the metal settle in the bottom. The next day (or at least 8 hours later) remove all the metal residue from the bottom and make sure that water from the bottom is not returning into the pool (valve set to dump). Oh, I forgot, you should first fill the pool above the average level so that when later you dump the water from the bottom, the level doesn't get too low.
The disadvantage of this method is that if you add new water from the same source to the pool, it will get brown again, so make sure (if you do add water) to add iron-free water.

2- The second method is by not using chlorine to maintain the pool. The disadvantage of this method is that in very warm weather, algae will probably be an issue, since hard waters have a tendency to form algae due to it's rapidly raising pH level. To prevent this from happening you have to make sure you use alguicide (preferably not made from benzalkonium chlorine since it will form foam and you'll have to dump all the pool water). What I use is hydrogen peroxide (about a cup of 35% technical grade hydrogen peroxide for every 1000 gallon once a week) plus the algaecide (as instructed in the bottle). But the most important thing if you use this method is to keep the pH level stuck at 7.2 (always fix the pH level before adding chemicals)
a- If the pool gets algae using this method, it's likely that the only way to kill this algae is by super-chlorinating the pool (yes, it will turn tea-brown) for a whole day (24hs) and then adding hydrogen peroxide back again. Keep in mind that chlorine and hydrogen peroxide they have a cancelling effect on each other, so you will have to use and extra amount of each to first cancel the other's effect and only the remaining will have a reading in the water. When super-chlorinating make sure that the pH of the water is stuck at 7.2.

Hope this helps lot of crying desperate souls

Any questions just aks!!

TheMartin


chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Solution for iron problem

Postby chem geek » Sat 28 Jan, 2012 19:11

If you raise the pH significantly, then you can deposit even more stains though on the plus side you can precipitate metals to help remove them. So this is a risky proposition. Using the BioGuard® Pool Magnet Plus® as a chelating agent probably helps prevent the staining that would otherwise occur from the high pH, though raising the pH is not part of their instructions. I'm glad it worked for you.

As for not using chlorine, that doesn't necessarily avoid the metal staining problem if you are using another oxidizer, even hydrogen peroxide. [EDIT] WRONG! See the later posts -- hydrogen peroxide is both an oxidizer AND a reducing agent and acts as the latter for metal stains if you don't have chlorine or other oxidizers in the water). [END-EDIT] The reason is that any oxidizer will oxidize ferrous more soluble metal ions into ferric less soluble metal ions where the latter can still stain. However, if you were using a hypochlorite source of chlorine to shock a pool, then that would raise the pH so the combination of chlorine as an oxidizer along with the higher pH would be more likely to stain than if you were to use hydrogen peroxide or a different source of chlorine such as Dichlor or Trichlor which would not raise the pH. So it wasn't chlorine, per se, that was the problem, but the type of chlorine you used and not lowering the pH before you added that chlorine.
TheMartin

Solution for iron problem

Postby TheMartin » Thu 02 Feb, 2012 21:01

Chem Geek,

It might be true that an elevated pH will somewhat stain the walls of the pool with brown-colored iron, but in my experience this is completely out-weighted by the fact that the hydrogen peroxide that you add later on will completely remove all of those stains previously produced.

On the other hand, you assure that hydrogen peroxide won't prevent the metal from turning the water brown while I know for sure that it's just the other way around. I have more than enough times seen my pool water turn tea-brown after a sodium hypochlorite shock and then the next day, just by adding a couple of liters of hydrogen peroxide (concentrated at 200 vol.) turn to crystal-blue in about 15 minutes. My pool has 8000 gallons aprox.

Then you say that by using hypochlorite source of chlorine together with an elevated pH is the cause of the water turning brown. That is also not true, since I have seen my pool water turn brown after adding hypochlorite chrlorine EVEN IF the pH of the water was extremely low (about 6.2). By the way, I do use that combo (the one of very acid pH with a very powerful shock of liquid chlorine) to completely kill all algae overnight without even having to brush. And yes, the morning after the walls will be stained with brown iron residue, but as I've said, that's when the 2.5 liter of 200vol hydrogen peroxide comes into play and completely bleaches the walls and magically turns the water back to a crystal-blue!! After that you can get you pH level back to normal by pouring enough dissolved caustic soda.

So your conclusion was in my opinion somewhat miss-leading, hydrogen peroxide DOES and WILL un-stain you pool.

Regards,

TheMartin
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Solution for iron problem

Postby chem geek » Mon 06 Feb, 2012 16:51

I forgot that hydrogen peroxide can act as both an oxidizer and as a reducing agent. So if there is no chlorine or other oxidizer present, then it can help to remove stains in the same way as other reducing agents such as ascorbic acid can do so. There has to be a chelating agent present or else the iron can get oxidized again, but your method has both in the water so the reduced iron should stay bound with the chelating agent. I will make a reference to your post from mine above since you are correct about this and I was wrong.

As for pH and chlorine, if the pH is very low and you get metal staining after adding chlorine (other than locally where you are adding it if you add it quickly in one spot), then the metal ion concentration would have to be very high in order for the ferric ions to precipitate or stain. There is no question that having chlorine in the water will convert ferrous ion to ferric ion, but having that then form oxides-hydroxides that stain requires a higher pH. I also have not read any other report like the one you are giving of a low pH resulting in staining after chlorine. Maybe the TA level was so low that adding a shock level of chlorine had the pH rise a lot anyway. Are you saying that the pH was low even after adding the chlorine and stains still occurred? I know that we've seen many reports of users who lowered their pH and the stains (if fresh) faded though using a reducing agent makes the removal go faster especially for somewhat older stains. Ascorbic acid works in two ways since it is not only a reducing agent but also lowers the pH.

Anyway, if hydrogen peroxide with lower pH works as well as you describe, I might have some people try that instead of ascorbic acid to see if it is at least as effective. Do you think it only works for fresh stains or does it also work for older stains? I haven't priced it for comparison, but hydrogen peroxide at $18 for one gallon of 27.5% (in BioGuard® SoftSwim® C) may be less expensive than ascorbic acid at $8-9 per pound. One pound of ascorbic acid reduces 4.8 ppm FC in 10,000 gallons while one gallon of 27.5% hydrogen peroxide (1.12 g/ml density so 1.166 kg hydrogen peroxide) reduces 64.2 ppm FC in 10,000 gallons. So the hydrogen peroxide is 28 cents per ppm FC in 10,000 gallons while ascorbic acid is $1.67. So if hydrogen peroxide can be as effective at removing stains, then it's far less expensive and has the advantage of not leaving behind any organics (hydrogen peroxide produces hydroxyl ion when it is used as a reducing agent so if eliminated from the water with chlorine it just produces water). One needs to add the cost of Muriatic Acid to lower the pH, but that shouldn't be very expensive. Thanks for the tip!

I also forgot to mention that the Pool Magnet Plus product you referred to is HEDP-based so is a better metal sequestrant and won't break down as quickly from chlorine. However, it doesn't completely remove the metal from the water so you need to keep adding it on occasion to keep the metal in solution since HEDP is slowly broken down by chlorine. Have you found anything to completely remove the metal from the water? Some people have tried CuLator , but results are mixed. However, with as much metal as it seems you have in your pool, it might be worth a try. I'd like to get more results about this product since in theory it is a permanent solution, albeit expensive.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Solution for iron problem

Postby chem geek » Sun 12 Feb, 2012 03:40

On the second method of not using chlorine in the pool, hydrogen peroxide is used in Australia as an approved disinfectant for some pools and spas though it isn't approved for such use by the EPA. You could use hydrogen peroxide along with Polyquat for a reasonable combination that would inhibit algae growth and bacterial growth as you describe. The algaecide you say to avoid is a linear quat and though less expensive, it tends to foam as you pointed out. The better algaecide to use is Polyquat and it is most economical in 60% strength (the ingredient is Poly [oxyethylene (dimethylimino) ethylene (dimethyliminio) ethylene dichloride] ).

If you could let us know if the hydrogen peroxide stain removal method works for older stains as well as new ones, that would be helpful. I'd like to try this out as an alternative to using ascorbic acid, but would like more info from you on when it works best.
TheMartin

Solution for iron problem

Postby TheMartin » Tue 21 Feb, 2012 16:41

Hi Chem,

I've been using hydrogen peroxide for the whole summer now and what I can tell you is that it certainly won't replace chlorine for disinfection. But what I do is when weather is very warm, I shock the pool once a week with hypochlorite chlorine and that's usually enough for killing whatever H2O2 hasn't. I leave it act for the night and the morning after I load the water back with H2O2.
To be honest, I don't know if H2O2 will remove old stains, probably it will in very high doses but I'm not sure, just guessing...

Regards,

Martin
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Solution for iron problem

Postby chem geek » Tue 21 Feb, 2012 23:35

Thanks Martin. I will at least see if we can use it in some metal stain situations where we would otherwise use ascorbic acid and see if it works as well. If it does, then it's a heck of a lot cheaper. Again, thanks for the tip.
PC103

Solution for iron problem

Postby PC103 » Sat 10 Mar, 2012 21:37

Hydrogen peroxide oxidizes iron, it does not reduce it.

Ex 6.3 The reaction between hydrogen peroxide and iron(II) ions

Half-cell reaction data:

(i) H2O2(aq) + 2H+(aq) + 2e- ==> 2H2O(l) (EØ = +1.36, reduction of oxidising agent with the more positive EØ)

(ii) Fe3+(aq) + e- ==> Fe2+(aq) (EØ = +0.77, less positive, so Fe3+ can't oxidise hydrogen peroxide)

Both the iron(III) ion and hydrogen peroxide molecule can act as oxidising agents, but hydrogen peroxide is stronger and so oxidises the iron(II) ion to the iron(III) ion. http://www.docbrown.info/page07/redox2.htm#6.3
PC103

Solution for iron problem

Postby PC103 » Sat 10 Mar, 2012 23:49

Iron in the +3 state can act as a Catalyst in the Decomposition of Hydrogen Peroxide. There are several proposed mechanisms, which involve oxidation or reduction of the iron (III) and then the reversal of the oxidation or reduction back to iron (III). I think that the net effect is that most of the iron (III) will end up as iron (III).

You might get some hydroxyl radicals as intermediate species, which could reduce Fe3+ to Fe2+, but for the most part, I don't think that using hydrogen peroxide would work.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Solution for iron problem

Postby chem geek » Sat 17 Mar, 2012 02:14

Hydrogen peroxide is BOTH an oxidizer and can be oxidized itself. There are TWO different half reactions that can occur (see Reduction Potentials ):

H2O2 + 2H+ + 2e- ---> 2H2O ..... E0 = +1.776V

H2O2 ---> O2(g) + 2H+ + 2e- ..... E0 = -0.695V

Fe3+ + e- ---> Fe2+ ..... E0 = +0.771V

So thermodynamically, at least, hydrogen peroxide can oxidize ferrous ion (Fe2+) to ferric ion (Fe3+), but can also reduce ferric ion to ferrous ion as well. Hydrogen peroxide is no question a reducing agent when it reacts with chlorine. I just don't know the reaction rates for these reactions and that is what really matters.

In fact, hydrogen peroxide can break down itself into water and oxygen gas, but this usually happens slowly unless temperatures are hotter or there is sunlight to produce hydroxyl radicals through UV photolysis.

So yes, the presence of iron may very well consume hydrogen peroxide as both oxidation and reduction reactions may occur, but what is required for a stain removal treatment is that it reduce iron so that a metal sequestrant can then bind to it at which point it doesn't react. So as a short-term additive to remove iron stains in the presence of a metal sequestrant to prevent re-staining, it may work. We're going to have some people try this out and if it works as well as ascorbic acid, then it will be recommended instead since it is far less expensive.

Return to “Pool Chemical Problems & Swimming Pool Chemicals”

Who is online at the Pool Help Forum

Users browsing this forum: No registered users and 11 guests