Hey Fishcounter...not sure if I understand your question right. Are you asking whether it's better to have a
sump in the tank or an external
sump? Or are you asking whether it's better to have the return pump sitting within the
sump or externally?
IMO, to have an external
sump means you're freeing up a lot of real estate in your display tank for corals, etc. Also, the pumps/skimmers/charcoal etc. doesn't always look so nice.
Concerning the pump, I think the aquarium pumps are built so well nowadays that I'm sure rusting isn't an issue.
If you want to avoid drilling holes in your tank, you could also opt for having a hang-on overflow leading down to your
sump.
Cheers!
