one of my dogs has a similar problem. from now and then he has a very liquid diahrrea,so the vet told me i could give him something that here is called "diaren", whic is basically nifuroxide+ attapulgite active...this one is really good, works like a charm every time. the other one is furazolidone, also good and it´s an antibiotic used to treat diarrhea and enteritis caused by bacteria or protozoan infections.
they are both great, and work fast...