Well anything with an impeller is going to make a brine shrimp shake, be it a filter or a powerhead. Even most of the sponges sold as prefilters are going to allow the nauplii through or at the very least suck them to it.
So far as a filter... Hmmmmm... an air powered hang on back! This one is so unbelievably simple, but it sounds way too complicated when explained. Lol, I guess I NEED to use that stupid photobucket account I *finally* opened
. I'll have a simple DIY for you pretty quick. The one thing to note, this would be for biological, mechanical really has no place in a tank growing out anything that small.
For the phyto as food, do a search for something called the "GEOSapper". I have the link around here somewhere, just incase I'll post that with the DIY.
When you get right down to it, as much of a PITA as it might be... Getting the UGF and gravel out will really help keep things more sterile. There by giving you more control.
Chris