I don't mean to ignore your question about alum/floc but if you've not begun draining your pool yet...DON"T!!! Not until you are certain the flooding you had has not saturated the ground around your pool. If it has and you drain your pool you will likely cause major damage. Hope i'm not alarming you unnecessarily but if there is high hydrostatic pressure around your pool from the flooding, draining your pool right now is NOT the thing to do.