My dog ate a balloon last night. Took him to the vet .?

I think your vet is ripping you off. I was a vet tech for four years and never heard of them double checking bc of gas. LAME! I would just let him eat normal food and don't waste your time and money on the expensive food. IF he isn't pooping normally or gets diareha then you should take action and take him back (or elsewhere). He is obviously not blocked if he can poop fine.