Perfect little brown circle stains

[arri]

Please help identify the source of this stain. I've included a quarter for scale. These little brown circles exist in a few isolated locations in my pool but in particular there are about twenty or so of them near the South West corner in the deep end. They look like little the remnants of little (1/8"-3/16") flat metal circles which stained the pool around their perimeter. However, I could not detect any change with over a minute of ground vitamin C in a sock having been massaged against one. It's almost as if the stain is below the surface of the fiberglass and somehow leeching through. A chlorine tab rubbed against the stain also had no visible impact. Neither has relatively vigorous scrubbing with a nylon brush. The stain in image with the quarter endured all test treatments for reference.

I've only owned the pool for about six months and have no idea how long they've been there. Any ideas? I'm convinced this is a metal stain, and would be willing to try a more vigorous method of cleaning it locally if suggested.

Water Chemistry:
FC:5 CC:0 pH:7.6 TA:90 CH:300 CYA:55 Temp: 89 F

 

[JVTrain]

To me, it does look very much like and iron stain. Like a steel circular object (washer, ball bearing...) was resting on the bottom of the pool and it moved over every couple of days, creating a new stain. I still have a stain like this, but a bit more amorphous from previous owner apparently letting a steel screw used in the pool light fall on the floor of my pool. The fiberglass should be impervious to water infiltration and I can't see any reason why there would be metal embedded into the fiberglass and leeching through. That is wan't affected by the vitamin C treatment is concerning though.

 

[mikemass]

Certainly looks like a metal stain.. Doesn't some parameter have to be extremely low for Citric Acid (Vitamin-C) to lift a metal stain? Free Chlorine perhaps? Sorry if that is incorrect, but I vaguely remember reading something along those lines here years ago. I never had metal stains so it was a passing read which didn't sink in.

 

[JVTrain]

Mikemass has a point there. If you lower the pH of the pool to 7.0 to 7.2, it will be easier for the AA to lift the metal stains.

 

[Texas Splash]

If you have some dry acid, maybe try that in a sock as well? But your pool is concrete and fiberglass at different locations right? I was thinking rebar from the outside, but wouldn't understand why that would be near fiberglass. I'll be curious to see how this one goes.

 

[Richard320]

Iron stains.

You ought to see what a nailhead will do. I had one that took a fly into the pool when the fence was redone and it left marks wherever it got brushed until i finally vacuumed it up. Bobby pins leave distinct marks, too.

Vitamin C will lift it. In my experience, sometimes it gets worse looking before it gets better when you set the Vitamin C on.

 

[arri]

Ok, so how do I improve my Vitamin C technique? I'm just using 1g Costco tablets which I beat with a hammer in a tube sock before rubbing against the stain. Should I try putting a plastic cup over a stain and creating a low pH environment in it for an extended (10 minutes?) period?

Is this just about using a convenient acid to lower the pH and lift the stain or is there something special about ascorbic acid here?

It seemed like the plume of weird water (seems like the refractive index was different or something) from the sock treatment wanted to diffuse into the pool rather than stay put

 

[Richard320]

I put the pills in a knee-high nylon with a smooth river rock to keep it in place and left t on the spot for about ten minutes.

Vitamin C is a weak acid and won't mess up the plaster. Stronger acids may.

 

[mikemass]

Here's the article on taking the Chlorine down to Zero

Ascorbic Treatment to rid Pool of metal stains

I guess this only applies though when doing a global treatment. If you are putting a sock full of AA on a stain I guess the concentration is high enough in that localized area for the Chlorine not to matter? Is this correct?

 

[arri]

Thanks, I've currently placed a plastic cup over a stain with about 20g of ground up vitamin c inside it and a dive weight on top to hold it in place. About every ten minutes I am moving the cup to scrub the spot with a toothbrush and replace the cup. So far, no response better or worse. I'll just keep going for an hour to see but expect the vitamin c to be fully dissolved and diffused by then.

 

[arri]

Success! I'm not sure how much longer than an hour it took because I had to leave for a couple hours, but it was truly gone when I did return. No scrubbing required. Now to streamline the method and start attacking the rest of them.

Thanks!

 

[mikemass]

Awesome job arri!!! What vitamin C did you use and how much did you crush it up? I have to attack some Bobby pin stains myself and can use the specifics.

 

[Texas Splash]

Outstanding! I was curious how that would work out for you. Nice job.

 

[arri]

It was about 20g of Costco's 1000mg tablets bashed up with a mallet that also have rose hips or something. I'd recommend starting with Richard320's advice regarding a nylons as my tube sock method was probably not best. Ultimately though it seems I needed far more time and/or saturation of the acid which I achieved by capturing the ascorbic acid in an upturned plastic cup held in place by a diving weight.

As I attack the remainder I'll experiment with tupperware or similar container to cover a little bigger area and possibly a little stronger acid depending on my patience.

 

[mikemass]

This may sound like a totally ridiculous question, but are they chewable tabs? I imagine chewable will break up better. I currently have a bottle of Rite-Aide generic chewable Vitamin-C but they are orange. I am concerned that the orange dye in the tablets may not be suitable. Is all chewable Vitamin-C orange? If this is not acceptable, I will run out to Costco later and get exactly what you used.

 

[Richard320]

This may sound like a totally ridiculous question, but are they chewable tabs? I imagine chewable will break up better. I currently have a bottle of Rite-Aide generic chewable Vitamin-C but they are orange. I am concerned that the orange dye in the tablets may not be suitable. Is all chewable Vitamin-C orange? If this is not acceptable, I will run out to Costco later and get exactly what you used.

I have no clue what makes them chewable nor how the dye will affect things.

I just used the cheapest plain tablets they sell at Walgreens. You're after the Ascorbic Acid and not all the binders and fillers and flavorings and dyes.

 

[wjr75]

Any kids around with a BB gun? Been there.

 

[arri]

Funny you mention that, my wife was speculating they were probably bb's as well given the former owners were from Wyoming and had young boys (and the house is in a migratory pattern).

I don't know anything about the chewables except that I avoided them thinking they probably had a bunch of stuff that makes them palatable which I didn't need in the pool.