Our oldest cat developed crystals about 8 years ago. He was eating Purina Indoor with occasional soft food. We switched him to Purina One Urinary Tract food which is a lot less expensive than the Science Diet or Royal Kanin. Our other two cats, one is a Maine Coon, eat the same food and all three get occasional wet food, Purina Naturals, and Greenie Dental treats for variety. No problems since.
My cat almost died. He had had problems before but when it came back, in 2 days he was “backed up” as the vet said and his creatin, I think, went up to...whatever...it was way high. Purina indoor, which I had already switched to and a Cranberry pill called Cranadine. Or something. 1/4 pill a day, 40 bucks for bottle lasts
120 days.
As I have said before here. He was one more 3 day vet stay from going to kitty heaven.
These problems are very aggravating for the owner, painful for the cats, deadly even. And very expensive to treat. As you and others have found out.