copied from wikipedia ...
" Carbon filters are most effective at removing chlorine, sediment, and volatile organic compounds (VOCs) from water. They are not effective at removing minerals, salts, and dissolved inorganic compounds."
Bio pellets remove phosphate and nitates. I would run them all if you can ,filter the water as much as you can. Do you have a sump? have room for a small bio reactor ? Dr. tims site sells some packages with a reactor , pellets and some benificial bacteria ... might besomething to look into.
http://store.drtimsaquatics.com/Mini...Kit_p_452.html