Hello again,
I'm very concerned about your dog.
Kidney disease is the #2 cause of death in dogs. Some breeds are especially prone to kidney disease, and unfortunately zus are among those breeds so your little part zu dog is genetically prone to this problem.
It is very serious when a dog with kidney stones loses its appetite and has frequent urination. These are signs of advanced disease. You don't solve this merely by changing foods. Your dog needs to see the vet for additional treatment for the kidney problems.
I suggest you print out the information at this page:
Monitoring a Dog's Health who has Kidney Stones
Read it carefully, then take it with you when you take your dog to the vet. You need to discuss the treatment options with your vet. Since I am not your dog's vet, haven't seen the dog, don't have his test results, etc. I can't give you any specific recommendations on what to do next.
Good luck!
jc