He's had this for a little bit and every home remedy I could think of doesn't help the issue. Groomer also has used different shampoos to no luck. He's a 5 y/o Aussie.
@brianhaskell I would definitely take to the vet... However, this happened to my dog and I freaked out and tried everything... Turns out it was just his skin changing. He went from a total pink belly to looking dirty to know it's all black... He is a real old man tho so depending on your dog's age it could be him just getting old...