I am glad you have a diagnosis. IBD can be very tricky to keep at bay depending on how severe it is. Pred is never a good med to be on, whether human or cat, but it does work and the key is to get the inflammation in his colon down. Although I am an advocate that diet does not affect a true IBD diagnosis, you may want to consider a diet that is very easy for him to digest. I do think the healthiest diet, with the least "junk" is key.
I am glad you brought him home, if a pet doesn't need round the clock treatment, then they normally do better at home.
So I am assuming the maroon discharge was mucous and blood????