Finally decided to upgrade from a 33g to 120g tank. Need advice on setting up filtration. Was looking at Eheim pro 4+ 600 and was recommended a under gravel filter also. The pet shop I got the tank from looked like the inlet and outlet of the gravel filter was connected to the canister filter. Is that the right way to setup a larger tank? Will I also need a new aerator or will the flow from the canister take care of that?