"BenignVanilla" sez:

"Just Me "Koi"" wrote in message
.. .
I vouch for Theron's response. You'll be sorry if you don't do both!
snip

This is where I am confused...if the bottom drain will remove anything that
comes to the bottom, why bother having a skimmer? Why not let it fall, rot,
get sucked and become food for the veggie filter?

I don't have either, but the answer is partially that some gunk floats.
Forever. Like cedar pollen in the summer... you get this film on the
surface.

My waterfalls fix that, as does my regular water change which I do by
overfilling the pond which effectively skims the entire top, but that would
be one advantage of a skimmer over a bottom drain.