
Hi again Jane,
the tapioca / white fish (I think caiplan?) as far as I know is a prescription only diet and should hopefully be entirely novel for him :)
Re colitis - the word is merely an all encompassing description for regularly occurring and indefinite problems re loose / runny motions. When coupled with sickness, especially regular bringing up of bile, it requires rapid investigation with firm diagnosis - thankfully something your vet has steamed ahead with :)
I don't know the ingredients of the RC diets you've been using - many dry completes, even those claiming to be "hypoallergenic" are something of a misnomer. They can only be so if EVERY individual ingredient is hypoallergenic to EVERY DOG - unlikely ;) With the diet your vet has chosen it is less likely that Floyd's system will have been exposed to those ingredients therefore all the more likely that his system should not flare up against them.
It sounds as though your vet is on the ball here - I hope all goes well and please update.
Gentle hugs to your lad, Teri