I don't have any experience with cats and crystals/urinary infections, and I am not a vet, but maybe a holistic food would help. I feed my cats, 2 female, 1 male, Holistic Blend which I buy a our local Health n' Harmony store. It is also available at Superstore, Loblaws, and it's ingredients are
cranberries(which is good for urine)
dried whole eggs
vitamin A acetate,D3,E, B12
Does Not Have:
animal by product
I stimulates the breakdown of ammonia in the digestive system to reduce stool and urine odour. Reduces urinary ph and provides low dietary magnesium.
It is for all life stages. :You can research it at www.holisticblend.com.: