I have a cat who had crystals, and he is on the Royal Canin SO diet. I just posted about him in another thread because he appeared to have a blockage last night, and I was concerned about the crystals returning. He needs another checkup tomorrow morning (and I'll update that thread then - I'm about to fall asleep right now), but right now its looking like he has some inflammation, but no crystals.
So I'm telling you that because when he did have crystals it was BAD. Between the crystals and the bladder stones it was an overall horrible situation. He's been on the SO diet since then. That was almost 2 years ago and even with this problem he is having right now, he still seems to be crystal free.
So while i understand the want and the need to feed your cats holistic food, I also just want to say that prescription diets are prescription diets for a reason. It actually really bugs me that there is so much stuff out there about how cat foods with animal by-products and fillers are bad for your cat. In a healthy, normal cat, I completely understand why you would want to feed a better diet than what is in most prescription food. But in a cat with a medical problem, the prescription food was created, tested and used to prevent that problem from re-occurring. Its not an actual medicine, but it functions like one. So to me, I may not like that animal by-products are one of the main ingredients, but you know what? Moses almost died from his crystals, and ever since he started eating the SO food hes been crystal free. So there is clearly something in that food that is keeping him healthy. I'm not against holistic food and the obviously healthier food, but just please keep in mind that its a prescription diet for a reason. I have heard way too many stories about cats with crystals who were given a prescription food that their owner took them off of for various reasons (cost...or the fact that they didn't like the ingredients) and the problem came right back. I know that there are definitely cats who have had crystals, and eventually gone back to a non-prescription food and have been fine, but you really don't want to mess with something like crystals. Its something that can get really bad, REALLY fast. So just because you personally don't like the ingredients, just remember that its designed to serve a purpose. I'll feed my cats animal by-products, grains and fillers if it keeps them healthy!
ETA: I do know that adding water to a diet for a cat with crystals is a good thing, but since it really is a problem that can turn very serious, very quickly,I'd really discuss it with your vet to see what he thinks. I'm not saying to always blindly trust the vet, but I'm saying to ask questions. Ask him why he recommends a certain food and not another food. Do some research on why the food is designed the way it is and the MANY cats that have led very healthy lives on it. There's more than one urinary diet out there, so you could have very well found a holistic one, but just don't switch to it without talking to the vet first. And just remember that what looks like bad ingredients to you, are ingredients that are keeping your cat crystal free. Good luck with this!