The iron idea came in to make the plants get extra iron and be lusher green, wasnt actually thought of because of the fish to be honest. and i got the idea from whats called the iron fish project, in africa in places where food was low in iron and stuff they made this little fish out of iron and called it the iron fish, it would get boiled in soups and stuff to add iron to them. strange concept for us to think of here since we dont have the problems those cultures do, so the ad for that gave me the idea of adding it to the water to make the plants greener. ... as for the fish, i dont think a little extra iron would hurt them, but it dont come back through anyways, what isnt used by the plants imediately dont make it back through the bed back to the water... in the plant bed i have the bottom lined with activated charcoal from aquarium set ups and then a layer of sand on top of it and a layer of gravel ontop of the sand that it filters through before dripping back into the pond. going to do similar for the ones i do with aquariums next year.