Deb, I've always been told to stay away from foods with a high ash content, especially fish-flavoured wet foods like fancy feast Whitefish and Tuna.
In the 8 years I've had Max, he has developed crystals 3 times all due to stress. Recently when I had renos done, he had a combo of crystals and a mild case of UTI that was treated successfully with antibiotics and Hills CD. For the past couple of years, I always keep a bag of CD and SD handy and every 3 or 4 months, I'll give him Hills CD for a couple of weeks, then put him back to MediCal Low Protein. Wether that's good or not, I don't know but I'd like to think that I'm being proactive and preventing any further problems.
I copied this off a website:
Should I Feed My Cat a Low-ash / Low Magnesium Cat Food?
A small percentage of cats are prone to a disease which causes crystals to form in the urine. This disease goes by many names, including feline bladder disease, lower urinary tract disease, or feline urologic syndrom (FUS).
It is thought that diet, particularly the levels of magnesium (a component of the ash content in the diet), may contribute to the formation of these urinary crystals. This has led to the recommendation that cats be fed diets which contain less ash and magnesium. Not all cats need to be on a low-ash/low magnesium diet, but only those cats found to be prone to this disease.
A good low-ash cat food should not contain a concentration of more than 6% ash (on a 100% dry weight basis). Magnesium should be no more than 0.1% and no less than .05% in a low-ash cat food. All low-ash/low magnesium cat foods that are certified by the Canadian Veterinary Medical Association must conform to these standards, and are designated with the term "low-ash" on the package along with the CVMA seal of certification.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand and strawberries in the other, body thoroughly used up, totally worn out, and screaming WOO HOO - What a Ride!
Sometimes the most real things in the world are the things we can't see
Until one has loved an animal, part of their soul remains unawakened.