Man, you've got a mess!

OK. You've got iron in the water. No idea how it got there, but it's there. Stain remover would have done NOTHING to algae; the fact that it make a positive -- if temporary -- difference pretty much is proof positive. But if it weren't, the clear to green transition on shocking is also a strong indicator of iron.

But, it sounds like you've got algae, too.

And, thanks to the pool store, you've got a giant witch's brew of unknown chemicals with unknown effects floating around in there.

=> Don't use any more stain remover for now. Stain remover TEMPORARILY re-dissolves the metal, but it doesn't permanently do anything, and it certainly doesn't remove the metals from your pool; it just MOVES them from the surfaces back into the water.

=> But stain removers ALSO consume chlorine, to the point that, if stain remover is present, chlorine is not. And, once you restore chlorine levels, all the stain remover is destroyed!

=> This creates a nasty see-saw for someone in your situation: killing algae tends to make the iron in the water come out as stains. But 'removing' the stains destroys the chlorine . . . and you lose any progress you've made against the algae!

I don't know what options you have, at this point. But here's what I'd recommend:

1. Maintain your pH to just barely below 7.0, to minimize staining.

2. If you have remaining algae, pull out your cover, and get your pool partially covered, to slow down algae growth.

3. Go to the pool store and find out EXACTLY what was in that mustard treatment. They are either ammonia based or bromine based. If they don't know, get them to open a bottle, and smell it. If it smells of ammonia, the question is answered. If not, you don't know since the ammonia products will NOT always have an odor. If necessary, buy another bottle, so we can test it and find out what's in it.

4. See if you can get some polyquat: http://pool9.net/polyquat/ Using it will help you control algae without making the stains worse. Do NOT use copper, which will just add MORE stains.

5. See if you can get any idea why you have iron in the pool. You need to find out if this was a one time problem, or recurrent one. Possible sources (in order of likelihood) are:
+ well water (especially if you have a water softener)
+ old iron city pipes (can intermittently release iron)
+ tanker truck pool fill.
+ low grade salt used with a salt water chlorine system.
+ low grade stabilizer (cyanuric acid)
+ ??

Good luck -- membership upgraded.