Took me a bit to figure this one out. After I tried every product on the market I found out I had bigger problems. After just a couple washes my clothes were a dingy yellow color. We decided to get a water softener and what a difference that made! I don't have to use a ton of soap or whitening products any longer. If you are having the same problem give a softener a try. We called RainSoft and in less than a week we were all set up, they even tested our water to confirm my thoughts on the iron
http://www.rainsoft.com/home-water-testing.cfm
Wish I would have thought about this a year ago!