Not necessarily a problem. I have iron deposits in my trout pond too and it doesn't hurt a thing. In fact what you may be looking at is iron bacteria working on the iron like in some toilet tanks. The iron bacteria actually feeds on the iron and breaks it down. There are actually some water treatment plants in Canada that use this bacteria to remove iron from their drinking water.

Any idea how many mg/l iron you have in your ground water?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.