I used 5 bottles of MM in my 27K gallon pool and the stains haven't reappeared. I also keep my ph around 7.5-7.6
It does say that MM will remove the metals from water if the correct procedure is followed. I still use the maintenance dose to be safe.
27K Gallon vinyl pool, 1hp 2 speed Hayward Super Pump, EC-75 DE filter, Stenner 45MPH22 liquid chlorine injection pump with timer control. Taylor K-2006 test kit, Aquabot pool cleaner. location SC PA.