Agreeing with John, as long as he doesn't look emaciated, I would keep trying, maybe just feed nothing for a day or two and then try pellets again.
About the Karma, think it works like you can give someone a "thumb up" if you found a post to be really good and helpful, this would increase the person's Karma. Same goes for the thumb down, just the other way round. Basically just something to play with ... I've clicked the button occasionally but I'm guilty of forgetting about it most of the time, lol.
(Oh .. think the buttons are only available if you've generated a certain amount of posts.)