Worried about my Coon

[Church]

Hi there everyone,
Just worried about my coon Church. We only have him a little over a month now and he is 5 months old. Since I got him he has been kept on the same dry diet as he was on at is breeders house with a mixture of wet- jelly food twice a week. I had him at the vets because he has constant diarrhea, he is 100 per cent except it turns out he is deaf and I'm worried about his weight, he does feel a little skinny and weights in at 1.8kg - Is this a normal-ish weight for a coon? As a first time owner this has me on edge.
He will be an indoor cat along with his brother bengal Whiskey (both are on the same food routines and whiskey is in flying form, gaining weight and normal poops)

If anyone can help me with info it would be great as google searches aren't really helping!!