Had our year old cat with crystals in the urine. Vet said the cause was the cat was not drinking enough water. We bought a water dish equipped with a pump for moving water to get the cat to drink more. Bought the cat medicated wet cat food from the vet store for urinary tract infection for a month to clear it up. Switched back to costco dry cat food. After that we haven’t had a problem. In our case, it had nothing to do with diet. Cats need a ton of water. We have two cats and together they drink over a pint every day.
Our cat had crystals even a blockage until we did two things:
1. Give him distilled water instead of tap water. This change alone may be enough. It was huge for our cat.
2. Changed from dry cat food to wet canned food.