Activated carbon removes organic compounds, but I don't believe it removes the inorganic fertilizers we use. A few of the trace elements might be reduced a little, but that should be all. I wouldn't bother removing it. If it has been there longer than a couple of weeks the odds are it is saturated anyway and won't remove much of anything.
I agree with hoppy but if it isn't doing anything I think it would be better to add some biological media, like the fluval ceramic cylinders for better bacterial growth. That is what I did in my canister filter. I have two of the baskets with bio medi. Maybe it doesn't make it a lot better but at least it's not just doing nothing. My 2 cents.
divy, most people do not use carbon on planted tanks as it doesn't do much and may remove some of the trace elemnts that we dose in well planted tanks. It does remove organic compounds but if you are doing regular water changes and removing any dead material from your tank it is not necessary.
I went ahead and took the carbon out and put in polishing pad, it's only been a day, really, but no noticeable changes, will keep posted. I'm not too worried about being without the carbon, I'm pretty anal about water changes. Really, though, this tank is so new (just BARELY cycled) it's hard to tell anything yet. I have both bioballs and ceramic rings so biologically it should be OK. I'll report any happenings.....