Dogs are sensitive to food changes and that's why if you switch them from one brand to another without doing a 7 - 10 day switch over you can get diarrhea. Putting them back on their regular food, one that their systems already are used to would stop the diarrhea.
The rule of thumb for switching brands is to use the 7 -10 day switch over where you start with most of the old food in the bowl and gradually introduced the new stuff until on usually day 10 they are eating nothing but the new stuff. Hope that helps. Good luck with the switch over. Oh yeah, btw, my mom feeds Blue to her guys and it has done wonders for her shepherd's allergies