You may want to look at the nano prefilters that LifeReef builds. I'm tempted to order one for my Red Sea Max and put a sump in.
Nano-Prefilter
Perfect for small reef or fish aquariums that don't require high flow rates.
Flow rate up to 400 gph (and anything in-between 0 and 400 gph) In other words it will flow whatever gph you give it.
Outer box: 4 1/2" x 3" x 9" high
Inner box: 4 x 2 1/2 x 6
Output connection 3/4"
Nano Features:
* AUTO-RESTART when power resumes, always 100%.
* No aqua-lifter pump or other device needed!
* All edges radiused and chamfered so you or your fish won't harm themselves on sharp edges.
* 7/8" diameter siphon tube.
* 1 1/2" of up/down adjustment of inner box.
* Inner box cannot be knocked out of vertical alignment.
* Long lasting and easily cleaned foam filter element.
* Will not overflow, even if foam element becomes dirty.
* 3/4" male thread output, hosebarb and clamps included
* Fits aquarium rims up to 1 1/2" wide and can also be made to fit acrylic aquarium rims or "Euro" style rims.
* Colors available: clear, black, and blue (inner box only)
* Sorry, no AquaSilencer available for this model.
Shown next to standard prefilter for size comparison.