Cats Rule Frog Water Fountain Filter

I own, and love, my Cats Rule Frog water fountain.  Even more important, one of my cats, who was getting dehydrated, loves it, so now he is no longer getting sick.  The problem is that the filter(s) provided with the unit impede water flow after being in place for just days.  This filter allows water to flow for much longer times.  I printed it in PLA here, and my cats seem fine.  I don't know what material to recommend if you want to print one at Shapeways.  Shapeways says that their ceramic material is food safe, but that material does not appear to be available at the moment.  Puzzling.