I hope he gets better.Well, Mr. Bumble is still alive. I brought him out in the run and watched him for a few minutes. He walked around a little bit, then just stood in one spot with his eyes closed. Now he is inside where I can monitor him better. I gave him some colloidal silver and tried to get him to eat some food. He was pecking at it, but didn't seem to actually ingest much.
I am no expert but I think giving him a rehydratation solution may be useful if he still has really bad diarrhea. On my sick hen I used a home made recipe before I could buy one, it was a mix in 250 ml water of a pinch of salt, two pinch of sugar, a pinch of baking soda (you have to use lukewarm water to have it dissolve properly).