using citric acid stains not gone

I am trying to use citric acid to remove brown stains from my pool. I have some questions. I have easy access to citric acid via my work. I can buy it very cheap, so I figured I give it a try. I still had chlorine in my pool when I started but since I have plenty of citric acid I figured I would start the process. My question is I added 10 lbs to 16,000 gallons of water. I still have stains and I still have chlorine showing ~0.5 ppm. The stains look a little lighter but I am not sure if that is wishful thinking. My question is should I continue to add more citric until the chlorine is zero or should the stains be gone? It has been circulating all night. I now am wondering if the stains are not metal. Also the stains have been there most of the winter so I am not sure if they are just really set into the plaster.

inground plaster pool with SWG current readings are
pH <6.8
chlorine 0.5ppm
TA 40
CYA ~60 ppm

Thoughts or suggestions? Also my Hayward vacuum is very brown stained as well. Will this treatment help remove the stains from this as well?

I'd recommend trying stuff BEFORE you dump a bunch into the pool.

Do this:

1. Put a vitamin C tab against a stained area, and leave it till it's mostly dissolve.
2. Buy a small container of "Iron Out". Put 1/4 cup in a sandwich baggie. Open it onto another stained spot, and then set a wet towel down on it, to hold it in place.
3. Take a chlorine tab (if you've got one) or a sandwich baggie of chlorine powder, and put it on ANOTHER spot. Do NOT leave it longer than 15 minutes, before your remove it, or brush it off.

See if any of these change the stains. Tell us what you find. Do NOT try to add stuff, till you've tested -- NONE of those things (ascorbic acid, sodium hydrosulfite or chlorine) are compatible with each other. Citric acid may work if ascorbic acid works, but try the ascorbic acid (Vitamin C) first.

What do the 3 different treatments show you? So if the chlorine tablet works but not others what does that mean? Same for other 2 options.

Thanks,
Ryan

Vitamin C (ascorbic acid) and Iron Out (sodium hydrosulfite) can both re-dissolve some metal stains, for example converting iron oxide (rust!) to soluble iron (Fe++).

Some stains are organic in nature, and unlikely to be affected by Vit. C or Iron Out, but are likely to be bleached by high chlorine levels.