Bichon diarrhea

Question
I have a 9 month old Bichon who has been on Blue Buffalo Chicken and Rice puppy formula for the past several months.  She has had diarrhea on and off with this food.  I have recently tried to switch her but haven't found a food that won't cause loose stool/occasional vomiting.  I have had her tested for parasites and is negative.  Could she have Giardia?  Any recommendations for a specific brand/ingredient of food?

Answer
Giardia can be tough to find at times.  I would have another fecal check done.  If she has it or another problem, changing food won't help.  

As for the food, most dogs will thrive on most foods, but no one food is right for every dog.  I guess keep looking for something different from the Blue Buffalo and different from what else didn't work.  I haven't seen any pattern.  Every food seems to have dogs that have problems with it.  If anything, I think I see fewer problems with the common brands such as Iams.