How old is he?
How long has he had diarrhea?
What and when did he eat last?
I am so sorry about the sibling.
Take him off dry food.. PLEASE READ:
He may have coccidia or giardia:
If so he should be treated with metronidazole (flagyl)
Try a few days of baby food chicken (no onion powder) with a tablespoon of infant rice cereal added to the jar. You can also add it to canned food as well.
He can also get the childrens lowest dose of Immodium a/d.
Please let me know how things are going. I hope he is better very soon.
Sincerest best wishes,