I've lost track of the days and number of times that I've had to deal with it this year. My troubles began in the summer last year and since then, I've been through almost two bottles of fish zole and about 250cc's of compounded metronidazole (50mg/ml). Seems like I spend my days following peas around, looking for symptoms and inspecting their poop, lol.I do know the cecal worm is a carrier of the protozoa, but didn't think the Metronidazole killed it. I could be wrong there and that would be great! I didn't know that it kills giardia... I figured it would kill the secondary bacteria and allow the immune system to control the rest (like when using Tylan for sinus problems). How long ago did you have to deal with blackhead (before it started showing up again)?