I'm not sure if carbon absorbs iron.
Trying to outcompete hair algae with macro is going to be difficult.
The only sulution I have had personally with getting rid of hair algae were turbo snails. I have heard lawnmower blennies are also good.
When i lived in Salt Lake, the local reef club had some sort of sea slug that they passed around. It apparently would free a large tank of hair algae very quickly.
I've also heard of a method that changes water chemistry (alkalinity i think). I'm sure you could find out more about this method with some searches.
HTH
