Chronic Inflammatory Bowel Syndrome (IBD) / Colitis
I feel your pain. I got Raven at 10 weeks old and he is now 14 months and has had diarhea almost his entire life until about 10-12 weeks ago. He came to me on a combination of Eukanueba Puppy & Bil Jac and had really loose stools - like soft serve ice cream. In an effort to firm up his stools I tried boiled white meat skinless chicken and rice and he started pooping liquid. I then tried California Natural and liquid poops started containing blood. I continued to try just about every high end kibble there was and all the time going to the vet weekly, sometimes more and nothing was working.
It was heartbreaking because he was growing and not gaining weight. I became very worried about his health, so I wound up switching vets 3 times until I found my current vet who diagnosed him with chronic Inflammatory Bowel Disease which causes colitis. My vet told me that IBD is a side effect of a compromised immune system, which has been the cause of various other immune related issues that he went through in his short life (demodectic mange & staff infection, etc). After over $1000 in tests to confirm chronic IBD and trying several prescriptions and prescription diets, my vet finally figured out the right combination that got Raven pooping semi-normal.
My vet recommended Eukanueba Low Residue Food, which is an RX diet that you have to buy at the vet that is specially formulated to produce less stools and be easier on the digestive system because the food is broken down to the bare amino acids. I was sick when my vet first prescribed this, because the kibble has everything you know you're not supposed to feed your dog (first ingredient is corn grits!). Even though it helped him, I wouldn't accept it as a long time solution, so I'd slowly try transitiioning him to CA Natural or Wellness and whenever I did the diarhea started again and got bad.
Long story short, I had to accept that the Eukanueba Low Residue was the only kibble that worked for him. He's also on 500mgs of Metronidazole daily(aka Flagyl), as well as 1 pepcid AC daily for acid reflux, which I didn't know he had until he started spitting up pink. After accepting the permanent switch to the Low Residue diet - Raven finally had his first solid poop in nearly a year. He has an extremely sensitive stomach and even licking snow can set him back to loose stools, but at least we found the right combination of food & meds so that he can poop solid. I hate the idea of having him on an RX diet and meds for the rest of his life, but I couldn't have him pooping liquid with blood.
I wish you the best of luck, but I'd suggest a quick google search on IBD & Colitis in dogs.
Good luck
-Annette