Rio makes some really tiny PH's. The 50 or the 90 would be good. If you want a propeller type of PH that would be more like the reef tank guys use, then the Marineland Maxi-Jet 400 might be the way to go, as it has a crapton of different attachments and 2 impellers in the box for not a lot of $$.
Here is the Maxi:
For my $, the Maxi's can't be beat...