OK.

Metals come -- usually -- from four places:

1. Well water --> iron or manganese.
2. City water pipes --> iron
3. Deteriorating pool equipment, due to mismanaged pool chemistry --> iron or copper
4. Copper algae treatments & 'mineral' or 'ionizing' pool gear --> copper

Usually, brown = iron or organic stains (oak leaves), and blue or green-blue = copper.

It sounds like we can rule out #1. But from where I sit, 2 - 4 remain possibilities, that have to be ruled out. Once you have eliminated all the metal sources, THEN you can see what it takes to clean up what you've got. That way, you won't have to worry about a re-occurrence.

You'll need to ask your water company about #2 -- their service manager will know, even if no one else does. But, #3 and #4 are all in your court. You'll need to

1. ID any metal pool equipment in the flow stream: metal pump, heater, ionizer or mineral product, etc. You should also check your lights, if any, for corrosion.
2. You need to check your CHEMICALS for copper; it's not only in algaecides these days, but also in trichlor tabs and other places you wouldn't expect. However, it's always on the label, though in fine print.
3. You need to check to see if there are any chlorine feeders UPstream of pool metal components, like tablets in the skimmer, an erosion feeder or a SWCG upstream of the gear.
4. You haven't mentioned any chemical measurements, so I'm guessing you don't do a lot of testing, and may depend on your pool store. You need ACCURATE measurement levels on your pool -- this testkit information page explains, and has pictures as well as Amazon links if you want to order there. Right now, you need a K-2006, and a salt test kit, if you have a salt system. You need to get a K-1000, or better, a local equivalent, and check your pH NOW, and make sure it's between 7 and 8.

Once you've done those things, we'll have a basis to figure out where your metals came from, and how to stop it. Replacing rusty screws over the pool is a good idea, too. Don't add any more ascorbic acid; you can't have chlorine and ascorbic acid in the pool at the same time -- they destroy each other. Continue to use HEDP -- but no more than the label recommends -- while you're collecting information. HEDP sometimes removes stains over time, and it will prevent new ones from being deposited.

You can order copper or iron testkits if you like, but they won't necessarily help -- we're not sure the copper kits will measure iron in the presence of HEDP, and iron tends to come out of the water, and land somewhere, pretty fast.

Anyhow, once you have your data, post it, and we'll go from there.

BUT, if you find obvious problems, like chlorine the skimmer, or upstream feeders, or pH tool low, fix those ASAP. You can use a floater for trichlor, and can raise your pH with borax from the detergent section of Walmart or where ever.

Good luck!