I didn't know this at first, as I feed him wet food mostly, but sometimes I give him dry food as a treat/snack when I train him.
I saw that his poop was so tiny and black, so I stopped giving him dry food and only wet food, and it went away.
I tried two different kinds of dry food, still...
He's 53 days old, he's really playful, he doesnt purr a lot, He only purrs for like 5 - 10 seconds at a time, longest one lasted for 1 minute and he was right next to me on the bed.
He's hyper when he wants to play, not pinky the cat's type of psycho hyper, just running and jumping around a lot...
