If you use carbon the key is to keep it meticulously clean. That means rinsing, cleaning or changing it once a week, depending on the factors of your particular tank.
While carbon is a two sided sword, the bad side is when it is left too long without the above maintanence, and all too often this is the case with the "lazy" hobbyist. And, YES, carbon can contribute to adverse water contitions if not maintained, even the best of the best.
So, bottom line, if you use it be prepared for extra maintainence chores.
This, as always, is my humble .02
HTH
Hermit