I have a couple of aqueons so I am familia with them. The cartridges are garbage & fall apart rather quickly. But theres alot of 'empty' space in them. Get a box of aquaclear 70 filter foam inserts & cut them to fit in any empty space in the filter. Mine are completetly filled with these. Since you just changed the cartridge anyway, throwing it out is not going to make any difference right now. You will need a test kit though to monitor your ammonia, nitrite, nitrate & ph because you are now back into a cycle & you will need to do frequent water changes to keep your fish healthy.