The 20HD is 8" long, 4" wide, and 4" high. It has a 3/4 MPT inlet and outlet. It draws 45 watts of power.
Looks like the Rio 200 is rated at 138 gph
. I'm thinking a Maxi Jet 600 with a venturi attachment (Premium Aquatics) would get the job done. It's rated at 160 gph
. I know an MJ900 (230 gph
) would do it. I'm pretty sure, with the 900, you wouldn't even have to get the venturi attachment. You could connect the airline right to the outflow on the powerhead with the included attachments. I have a small skimmer that came with a Rio 200. I got an extra 200 with it (all used to be fair about it). Neither of the Rios would run for more than about 15 minutes...I ended up installing an MJ900 with the venturi attachment and haven't had a problem since.