I certainly wouldn't remove the AC
. It is so easy to clean you can do it every water change and the inserts last for many years. I wouldn't add the cannister. Keep in mind that adding another filter will not reduce the need for water changes, it will just give you one more filter to maintain. If it was me, I would have only the AC
If you have one filter that is adequate (0 ammonia, 0 nitrite) and you add a second they will split the load, and your nitrate number will remain the same. As well, every solid surface in the tank will support nitrifying bacteria which aids in biological filtration.