Vet called back and said she's prescribing 10 days worth of Ronidazole and then wants to do another fecal test in two weeks. Hopefully this medication isn't too hard on his system and takes care of the problem in one shot. I'll be sure to offer him some extra hydration to help protect his kidneys. Strong meds make me nervous after Dundee but this seems like a logical course of treatment (and I saw the flagellates myself) so I'm hopeful. Meds should arrive from Wedgewood in a few days.