I know that formula poos are definitely more smelly than BF, but I don't know about runny. When Nina went onto formula, they were more the consistency of soft cement. If the poos are 'mucousy', I would ask your paed as this can be a sign of lactose intolerance. Some formulas have different ratios of casein & whey, and it also depends on the type of protein in the formula. Some babies have an intolerance to cows milk protein, not simply lactose as such.

If you are worried, I would talk to your health nurse or you GP/paed.

Good luck!

Julesy