Pearfish, I've been dealing with the same problem. I just received the advice pasted below from another member (ThRoewer, I think is the name) who has been helping me with a couple of issues lately. His advice has been very helpful so far, so I just ordered this. The shipping for me was next day for $3 or $4 more!
"The medication that worked well for my percula was API General Cure.
It's a combination of Praziquantel and Metronidazole. After two doses the white poo was gone. "