So I have a well established(4 months) 75 gallon tank. I perviously had a 110 gallon tank. I currently run two canister filters on my tank. One is filled with bio media and the other is filled with polyester that polishes my water. Ever since I have been doing the whole "tank" thing(3 years now) I have never used any sort of carbon, amonia remover, or anything of that nature and have never had any issues. I do regular weekly water changes that go from weeks 1-4 and starting with a 10% change in week one and ending with a 40% change in week 4. The only things I add to my water when conducting a water change are Seachem's Prime and a Stress coat. Now am I doing my fish a disservice by not running anything else in my filters? They seem happy. Never had any sickness issues and the fish seem to like it the way it is.