Sponge filter need
--smallest sponge filter you can find
--airline tubing (silicon, floppy type is best)
--air adjuster valve ($3)
--one-way check valve ($4)
--airpump Tetra Whisper 10 works good and is comparably quiet.
That Hydor you found on Dr F&S is way too big for what you need. This is their smallest model (the one I use). [ame=http://www.amazon.com/ATI-SPONGE-FILTER-LUSTAR-GALLON/dp/B003I5QRWO/ref=sr_1_1?ie=UTF8&qid=1385035851&sr=8-1&keywords=Hydro+mini+sponge]Amazon.com: ATI HYDRO SPONGE FILTER MINI LUSTAR HS900 7 GALLON: Pet Supplies[/ame]
Hydro is top-of -the-line. You can use an airstone for more efficiency and less disturbance.
Here's a cheaper knockoff which works just fine. [ame=http://www.amazon.com/Jardin-Aquarium-Cylinder-Sponge-Filter/dp/B005LMQCW2/ref=sr_1_fkmr0_3?ie=UTF8&qid=1385036189&sr=8-3-fkmr0&keywords=CAF-10+sponge+filter]Amazon.com: Jardin Fish Aquarium Mini Cylinder Soft Sponge Water Filter, Black: Pet Supplies[/ame]
This is the smallest I've seen.
Internal Sponge Filter CAF-10
Someday, I promise, I'm going to write an article on how to set one up and operate it.