an XP1 should be more than sufficient for a 5 gallon tank. it's what i plan on using for my 7.5.

oh...

do a search ebay for red sea CO2 paintball... youll find a decent, and relatively inexpensive (considering the alternatives) CO2 injector for planted aquariums. i probably won't mess w/ lilly pipes and that not, just use the red sea gizmo. a well planted tank has all that stuff hidden anyhow.