or you could just take the medium out of the old, stick it in the new, and be good to go.
-edit- you might also have a green water problem. Look into getting a UV
in-line sterilizer that works with canisters. I had this problem in my 125 cichlid tank. Water stays crystal clear now.
125 malawi cichlid, 110 Discus, 75 reef, 30 reef, 27 reef, 4 planted