Welcome! Sounds like you sure know your stuff. We're glad to have you aboard!!!

Wellness is a great food. Since you are switching him to such a good quality food (pretty high in good/meat protein) and he is still a puppy (sensative digestive system) he may take a week or so longer to adjust to the new foods. Anything high in protein will usually cause softer stools & may take a little longer for them to firm up.
As long as he has no other effects it's all normal.