I agree, carbon has not helped me either. What did the trick for me was Purigen by Seachem. Its a macro-porous polymer. I added a little filter bag to my system and within 12 hours my tank was clear. Clear actually is not the right word. The water is practically invisible. A friend who saw the before and after joked that my tank now had better resolution than reality.
And another great thing about the stuff: it changes color from beige to dark brown when it is used up. So no guessing about when to exchange it. It also can be regenerated by a really easy procedure and be used over and over. That makes the higher initial price (compared to carbon) quite worth it. As a result I kicked all the carbon from my filters and replaced it with Purigen. My water quality has been stellar ever since.