Carbon removes chelated fertilizers (like Iron). I know when I ran iron tests, it had removed the iron in one day. It may remove more than that, but I've never done the tests. If you're looking for a replacement for carbon's actions, I use Seachem's purigen and it works very well. Though in general most of what carbon/purigen is designed to remove is good for plants anyway thus you don't want to get rid of it. Carbon still is useful to have on have for times where fish are dying and your uncertain whether it could be a toxin. It got rid of the toxin I had in under a day.
Thank you guys, I don'tknow why the water in the tank doesn't stayed clean, Do I need a different filter, my tank is a 60 gallon tank with an aquaclear 110, running CO2 and the substrate is a mixed of natural gravel and eco????