Heres a list of what i can remove and how well.
Absorption Potential of Various Substances by Activated Carbon
High to very good
Arsenic, bleach, chloramine, chlorine, chromium, colors, dyes, gold, insecticide, odors, monochloramine, tin
Good to Moderate
Acetic acid, cobalt, detergent, hydrogen sulfide, mercury, ozone, potassium, silver, soap, solvents, vinegar
Copper, iron (not chelated), lead nickel, titanium, vanadium
Low to None
Alkalinity, ammonia, barium, carbon dioxide, hardness, copper, manganese, nitrates, selenium, molybdenum, zinc
Even good carbons add some phosphate which I beleive is used by some plants??