Before Grain and Tiki cat for a 8 week old kitty

Ok so I have had my mother cat who was a foster on wellness kitten food. Well I am keeping one of the kittens and gave him BG and Tiki ct for a wek and his poohs did not stink.
Now he is back on wellness and they are funky.
Why is this?

And can he eat Before grain as a kitten and Tiki Cat canned. He will eat tiki cat canned as a adult along with a dry food once we find out what but is it ok to feed to a kitten.

What is the best grain free food for cats/kitten I want him to eat grain free food.

Oh boss is a male and he will be fixed in a few weeks
Does fish make a difference for boys?

I don't feed fish to cats (except if it's like the sixth ingredient), especially males. It's not a natural food in a cat's diet, and it can cause some pretty serious diseases in cats. Before Grain is an excellent food, though. Good luck! BTW, Boss is adorable. He looks just like a kitten version of Fatty.