Use of Oxalic acid

rcsong01

New member
Jun 28, 2010
1
Hi,
I have read all of the posts regarding the use of Oxalic acid you have posted. Thanks to you all for the information. I have a simular problem and have been using OA to combat a brown stain in my pool as well. The OA works great in my 20k gal pool 4 lbs and it is perfect. Problem, even after adding the proper sequestrian agents to filter and backwash the metals. My stain occurs over again slowly after about a week or two. Perhaps Iron cannot be pulled out completely? Is it ok to treat with OA that often? I will check my steps and plumbing for any signs of corroding metal, other than that not sure where it comes from. Perhaps when I add water to the pool?
I use Bromine, and I keep it low and rise very slowly to stop from oxidation. I also have a heat pump, but I do not think the stain is copper. Would copper make this light brown stain?
PH, Akalinity, hardness all fine.

Any ideas or help here would be welcome.
Thanks
Richard
 

JasonLion

TFP Expert
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LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Welcome to TFP!

Sequestrant doesn't remove metals from the pool, it binds to the metals and holds them in solution so they can't cause stains. Unfortunately, sequestrant breaks down over time, so you need to be constantly adding more, otherwise the stains will just come back, as you have seen.

Light brown stains are almost always iron.
 

Emare123

New member
Jun 12, 2011
1
(I know this question was posted last year, but I came across it when searching for more info on oxalic acid, and i thought it might be helpful to add this.)
I bought a bottle of the pool metal stain treatment and it contained oxalic acid. Unfortunately, I threw it out already, but I think it might have been united chemicals pool stain treat. My bottle said if you have a heater, it has copper in it (all heaters?) and you shouldn't use the product because it will eat copper. So, I'm not a pool or chemical expert, and the bottle didn't list any other ingredients other than oxalic acid, but I've read that oxalic acid isn't a metal sequestering agent, but the product removed, chelated, and sequestered, so maybe it had more than just oxalic acid (or the Internet info i read was wrong?), but if you have a pool heater, with copper, maybe before using it, check to make sure it won't eat through your heater just in case. (or is it possible to bypass a heater?)
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Welcome to TFP! :wave:

I don't think it is the oxalic acid they were worried about with regard to copper in the heat exchanger. It might be the low pH of the treatment overall that is of concern (oxalic acid is low in pH, but there are other chemicals that can also lower the pH). As we've already noted, oxalic acid isn't a good bulk treatment since it precipitates with the calcium in the pool. As a spot treatment, it may be OK.
 

X-PertPool

TFP Expert
In The Industry
Jun 12, 2009
1,385
Exeter, PA
I've noticed some calcium precipitation with oxalic acid. What is a better choice for bulk treatment? Ascorbic? It's kinda expensive. But if it's my only choice how do they compare in strength?
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Ascorbic acid is your main choice though some have talked about using citric acid which is less expensive, but I don't think it's as effective and as described in this paper, it forms chloroform (a disinfection by-product). Ascorbic acid should be reasonably effective.
 

JasonLion

TFP Expert
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LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Several people have had good results with citric acid, but they seemed to need to use somewhere around double the amount compared to ascorbic acid.