I have a bad iron/rust stain all the way around the liner of my above ground pool. It is 24'x52" so about 14000 gallons. I have put 3 bottles of metal magic let it run for 3 days with somewhat positive results. The bottom cleared up some but the sides were still bad so added 5 lb of vitamin C acid not really any effect un less u place on a sponge directly on the stain. What else do I do?