I agree with Marc. I've got the ER 250 on my 150, and it does a pretty good job.
I just rebuilt my sump to use the sections a little better (view
here or
here for detials), and am thinking a bit of doing frags in the middle section (water now flows from skimmer - frag section/settling area - return section). The middle section should be easy enough to siphon unless you really load it up with frags.