If your puppy's having diarrhea there are a few home remedies you can try but before you do, contact your vet and just get their advice on it.
Some home remedies would be boiled chicken and rice which is something that you would normally do if the dog is having a stomach irritation. Just go with something nice and bland.
Also canned pumpkin, not pumpkin pie filling, that's very important, not pumpkin pie filling but canned pumpkin is actually really good for their digestive system and can actually bind up some loose stool if you're having an issue.
If it seems to be something that's progressing even though the dog has had a clean bill of health from the vet and he has no parasites and nothing seems to be the matter, it could be the food that you're feeding him, it might be a little too rich.
You want to make sure that you have a food that is high in nutrients, really low in by-products, really low in grain but also just doesn't pack so much of a punch that it's running through the dog. So you might have to experiment with some high quality food brands.
Obviously get your vet's opinion on the situation before you do anything but if you do have a dog that just kind of has a sensitive stomach, has a clean bill of health from the vet but does have occasional soft stools, a little chicken and rice or using the canned pumpkin. Like I said, you can actually fill Kongs with it, you can freeze it in Kongs. Dogs really dig it and it has a tendency to bind up their stool nicely but not too much.
So that would be my advice on how to treat diarrhea in puppies.