I went through the same thing with Smokey. My vet prescribed put Smokey on the S/D diet and we also tried the C/D diet, but none of those foods worked for Smokey. My vet also gave Methio-Form, it is a chewable tablet that can be put directly into wet food. This helped enormously but unfortunately Smokey ended up with the "operation" and since then I have had NO problems with the crystals.