What can help rid my ferrets of diarrhea?

I have 3 ferrets and they all have diarrhea. They have constant supply to fresh water, they eat Evo kibble, don't have access to anything they are not supposed to eat, have baths as needed, get regular nail trimmings, have clean ears, eyes, and teeth. They are overall spoiled, but healthy ferrets! Is there anything I can do to get their bodies working properly so they don't have diarrhea?