I never use carbon in any of my tanks unless I am trying to remove meds. The carbon takes nutrients out of the water that your plants use. So if you have live plants carbon is not suggested. I have 3 aquaclears and what I do is I put the AC spong in then I just double up on biomedia. The more biomedia the better, you can also sandwich other things between the biomedia and the sponge. For instance I keep coprisurb I think its spelled in my shrimp tank to keep the copper out since it poisons shrimp.
Then I use purigen to replace carbon in all of my tanks. You don't need it, I just use it to polish the water and make it clearer. Purigen works like carbon in the way it cleans the water but it does not remove the nutrients, its like the planted tank version of carbon. It is a little pricey though, what I did is purchase a liter of it online then order seachems' the bag. Its a very expensive bag but the only one with a fine enough mesh to keep the purigen from coming out, its like sand. I then used my vacuum sealer to make individually sized bags so I can use it in multiple tanks instead of just one big batch.
I keep the carbon that came with the aquaclear on hand just in case I need to use medications in my QT tank, I would use the carbon to remove then after treatment is done.