You're right -- since the Metal Remover is ascorbic acid (vitamin C!), we don't have to worry about HEDP. (And, since you have chlorine, it's all gone, too.)

Your contractor knows your pool. Ask him again, and confirm that it's safe to drain as far as he said, and then do that -- NO FURTHER!

Since the mess is just alum, that will eventually filter out. Draining it partially should reduce the problem to a more manageable level. I'll call someone, and see if anything will speed that up.

Do go ahead and remove & replace the two 2" of your sand, which should also remove the Fiber Clear. And do remember you MUST keep your chlorine levels up during this entire process or you WILL have algae again!