When Bella was a little over a year and was diagnosed with struvite crystals, I went all the possible routes to help her but finally ended up with a perscription food from Royal Canin called SO. Since she's been on that canned food, thankfully, she hasn't had a problem.
I would avoid Royal Canin SO at all costs as it has less nutritional value than Beneful! Not too mention that when I had my two older ones that it nearly sucked the life out of the younger of the two and there were always recurrences of crystals/stones + lots of vet visits.
Just 2 weeks after switching her to a grain free food with the addition of the Wysong pH supplement she was a new dog. She got her spunk back where before she laid around more like a senior dog when she was only 3-4 years old. Also, no recurrences of stones of crystals for 4 + years till we ran out of the supplement and I screwed up and thought she was ok without it.