Phillbo, I hope you are in better shape than your pool

I HOPE that you realize the danger in draining an in-ground pool and have taken the possibility of it 'floating' into account.

Hard to kill areas of algae/ 'bio-nasty' can be treated with a concentrated dose of chlorine with the water still in the pool -- it's tricky but I can give you a few suggestions on it.

If your plaster is in that bad shape, can you afford a recoat?? If not, treat the areas and do a quick recoat yourself while the pool is empty.

If you need more, we'll help.