So I've had Leo for about a week now, and just last night his stool looked very soupy. And this morning as well. It's a light brown, almost yellowish color. I highly doubt that he's sick, so I`m wondering if it's the food. I`m a first time owner, trying to do this right but, for the past few days his stool was well formed and dark. I feed him Totally Ferret, when he used to be on Marshall's more than a a week ago. I've also added a few bits of raw meat. Am I doing something wrong? Or should I throw in some of his old food? Or a little bit less on the raw meat? I wasn't giving him a whole chunk before, I just started and his stool got soupy, so I`m guessing that what did it. Of course I cut the raw meat into small little pieces, and he seems to REALLY enjoy it.

Other than that, he's playful, happy and energetic. I just want to make sure and see if I have to take a few steps back.

His tummy is adjusting to the new food.  You can add some marshalls back in, if you want, or just go with the loose stools for awhile until he gets used to it.

Yes, I'd say it's just his stomach adjusting to the new food.  Snapper is rght; you can add some of his old food to ease the transition, but I wouldn't worry with it.  He will improve in a few weeks.  It took my ferrets 4 weeks almost.
 
BTW, I love your Cowboy Bebop avatar ;)