Try mixing 80% of the old food with 20% of the new food for 2-3 days, then switch to a 60:40 ratio for a couple days, then a 40:60 ratio for a couple days, then a 20:80 ratio and finally 100% new food. The whole process should take about 1 1/2 to 2 weeks. This is what I've did whenever I've had to switch food with my two. Its time consuming to measure it out everyday but it is totally worth it..not having runny poo is good thing
