Oh gosh!! That sounds awful!!! I’m sorry!! I would definitely try Purina One or Dog Chow. Often times the Pro Plan can be too rich for a lot of dogs. It’s got a lot of fat and protein which can be great for working dogs but not necessarily pets. I love Purina One personally but we loved Dog Chow too. And they have a lot of different kinds you can try if one doesn’t work. Although Purina One also has a lot of kinds.Dorie is currently on Wellness CORE Digestive Health Chicken and Brown Rice and has been on it for at least a year. Her poops are semi-firm (which is a big win for her) but she seems to have bad acid reflux. When she has diarrhea she gets Purina Pro Plan Veterinary Diets EN Gastroenteric Fiber Balance. This food causes her anal glands to fill up and leak.
I believe we've tried another food from the Purina Pro Plan line, one from Blue Buffalo, Diamond Naturals (which is what Luna is on), Purina Puppy Chow, and a couple others. All of them gave her diarrhea or "soft serve" poop and I introduce new foods VERY SLOWLY.