So what is your plan to remove the iron? 4 hours with a little polyfill is not going to put a dent into it. You either need to do a water exchange of at least 50% right after AA has lifted the stains or invest time into letting the polyfill absorb the metals. If your fill water is going to have a decent amount of iron in it, you will just have to be patient with the polyfill and live with some stains for a while. You will need to get creative to pass as much water as possible through a large quantity of polyfill, which is why some people have used 5 gallon buckets.