So glad you guys are back

Might as well be among the first of the needy !

Background, have a small fiberglass pool that uses a heat exchanger and a zone off our our boiler for heat. Works great. Last year I noticed that below the water line was becoming stained and couldn't figure out why. Tried metal out, jack's magic and a couple of other products with no results. Fast forward to now, pool is drained down about 1/3 and the staining is really bad, about the color of oak from the water line down. Figured I'd try some muriatic acid on a test area and it worked great for bringing it almost back to white. Gave the test area a good rinse when I was done.

I found the source of the metal and it was a couple of galvanized pipe elbows off the heat exhanger, they were very badly corroded inside. Replace them with pvc.

Well that a lot of baggage but there are a couple of questions coming:

I want to drain the pool, dry it, spray it with acid, rinse it and then refill it. Not much ground water underneath me, yard is quite sloped and the pool is at about mid yard. Anything to be aware of when draining it?

Next, muriatic acid and fiberglass, good idea or bad idea? Any precautions other than glasses, gloves and ventilation?

Last one, I'm sure there'll be some metal in the water still when I'm done, how can I get that out and prevent staining in the future?

Thanks for any help.

Mark