Depends, Scott. Is it going to have fish/wildlife in it or just plants?
Is it in full sun, or does it get some shade? If it's in a spot that gets
a lot of sun, and if you're going to throw a few fish in (which I think we
all end up doing eventually!) You'll probably want a filter to keep it
clear. But go back and read some of the old posts about D-I-Y filters....
it would be easy enough (and cheap enough) to just rig something up on your
own, rather than buying one. Something as simple as poking holes in a
small plastic container, wrapping the pump in quilt batting, and sticking it
in the plastic box!
Sue

Only a couple fish, lots of plants, good surface coverage no filter would be
needed at all.
Colleen