A couple weeks ago I noticed a bunch of small red spots in my pool. I've seen similar stains before and I got the sick feeling it was rust. This is a white plaster pool and I've heard rust in plaster is the worst to try to get rid of. I am trying to save the pumice stone as a last resort.
They look black on my computer but they are the typical deep dark red color of rust. Though you'll notice they are not a spread out radial kind of stain you sometimes see rust form in.
The first thing I tried to do was take a 3" Trichlor tab and use a tab holder (it's a tool you can use to hold a tab at the end of a pool pole) and rubbed against the stains. The tool really only lets you rub in one direction, and it leaves a sort of snail trail of chlorine dust where you rub it. So I made a few swipes at the largest stains in that picture, and let it sit there for about 15 minutes. If there was any difference in the stain, i twas too light to notice.
Feeling more towards the idea that it's rust, I tried a bit harder with the Vitamin C. First I tried grinding up the pills in a sock, and then setting it against the stains and holding it there with a pole. I also tried leaving a pill on top of the largest stain overnight. I'm not sure if I noticed any lightening or not. If it had an effect, it was much less than I was hoping for. The picture is of after all this and as you can see, the large stain there is still very dark.
Here are the chem stats:
Is it possible these stains are anything else that would not respond to either the tab or the vitamin C? This one has me stumped and frustrated. This pool was previously near perfect save for some black algae here and there.