I hope that everything went well for Ash and that he'll be able to come home soon. I'm sorry to hear that he has a kidney problem but hopefully it's been caught early. I don't know much about kidney diets but I have read and heard that cats need more fluids so I would think that you might need to start feeding him more wet food mixed with some water to help give him more moisture. Ash will remain in my thoughts and prayers. Please take care.