Hi I Have A Question. One Of My Dogs The

Hi i have a question. One of my dogs the other day had diarrhea that looked bloody but he ate a red gift bag. (He eats everything) but he still has it and 3 of our other dogs have diarrhea now ( none of them have blood). They acr fine playing drinking but just yucky poop. We are wondering if their dog food could have been bad. We changed back to an old one today to see if it helps. What do you think