My first reaction was meat. I did a search on CZ but could not find any information. I don't give my dog any grain, I read through all the dog food at chewy.com and a lot of people want grain free dog food.
You will find information on the regular internet and not only from vets but also alternative health.
Here is a diet:
Diet for Dogs with Bladder Stones

Dietary therapy is useful for treating and preventing struvite stones in pets. Since the struvite stones form in urine with a high pH (alkaline urine), diets should help to maintain a low pH (acidic urine). Diets with animal-based protein sources are most important in maintaining an acidic pH, while vegetarian or cereal-based diets are more likely to cause and alkaline urine. Homemade diets are preferred for dogs with chronic bladder disorders such as bladder stones. If processed foods must be fed, most holistic veterinarians prefer canned diets, which contain large amounts of water, rather than dry foods.

Important: Before you start to feed your dog or cat a home-prepared diet, it is strongly recommended that you discuss your decision with your veterinarian or a holistic veterinarian. It is essential that you follow any diet's recommendations closely, including all ingredients and supplements. Failure to do so may result in serious health consequences for your pet.