We have a blue heeler that will only eat diamond dog food, we can buy it at our local Co-Op or Tractor Supply. I agree its not the best food but he is a heeler and very very active around our farm. It works for him but I would go very far in debt to buy good dog food for my yorkie. In fact its a fight with hubby when we buy dog food. He is always telling me I am NUTS for buying such "expensive" dog food for a 3 pound dog. I just tell him to shut up and write the check.
He loves her and he knows it. Long story short.....I would NEVER feed my yorkie diamond dog food. Mine gets soft food in the mornings and hard food at free range all day. She LOVES her soft food but we only do it once a day (vet says). Hope you can figure out the problem.