Food for urinary blockage, picky cat

Hi guys! I brought my Levi home from the vet 1.5 days ago. The first night he did fine, he was peeing again, and had a good amount of the prescription food. Well he hasn't eaten since, except he got into my roommate's cat's food, which is not formulated for him (I decided to keep him in my room when my bf and I aren't home to be sure he's not getting into the wrong food, but I guess my bf didn't understand that and left the door open so the cats "could play"). Anyway, that happened about 15 hours ago and he hasn't eaten since (besides me giving him salmon right now because I don't know what to do).
I know he's being picky because he still tries to go for the other cat's food. I have wet and dry food out for him (the Hill's c/d) and he won't eat it. Just an hour ago he was scratching on the plate I had it on, aggressively. I'm supposed to still be sleeping lol. Anyway, thought I'd look for some advice here... Will be calling the vet in a couple of hours when they open. Thanks for listening.

With crystals issues there are so many factors and there is no one size fits all.  With a blockage they often initially give a food that dissolves crystals but if he won't eat it then it can't do anything for him.  Not eating will also cause a serious liver issue called hepatic lipidosis also known as fatty liver.  Hopefully your vet can give you some suggestions.  I know some kitties after the crystals are dissolved can do well on certain regular wet foods, others do fine on any exclusively wet diet, others need the prescription food.

It really is impossible to give you a generic one size fits all plan.  He does need to eat though, that is true of all kitties.