Poor Storm. Some cats simply NEED to eat the prescription diet......forever! And yes, all your cats can safely eat it so then there would be no trouble with switching bowls.
Just for info, crystal formation and a UTI (urinary tract infection) are different. The cranberries might help keep bacteria from growing, but I don't think they do much to prevent crystal formation.
Using sub-Q fluid should help flush the bladder, crystals and all, but it may not be necessary. Your vet will let you know.
Now, don't beat yourself us. Many (if not most) of us have make an inadvertant error in judgement, I know I certainly have.
Storm will get better soon, do not worry.
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