Okay, when my little guy had soft poo here's the checklist I used. First, empty the water bottle, clean it again & refill. Dust or bacteria could have gotten in the water & that could upset their system. Next, remove pellets & just give him tons of hay. This will keep the system going & have a lot of fiber. Also you could try giving a plain shredded wheat as well in replacement of pellets. I can not stress enough how short-term of a resolution this is for you. If it doesn't improve within 24-48hrs I would go to the vet. Finally, a lot of vets will let you drop off stool samples to be tested without having the animal seen. Good luck!