Twelve a day is the ceiling. You can take more, but there isn't any proven benefit beyond that, and the side effects worsen. My doc claims there's not much benefit beyond 10 but to experiemment with 12 if I want.
I'm taking 10 a day right now (5,000 mgs), five in the morning, five at night. I haven't noticed any benefit to my colon, but it has helped with the UC-related joint pain, esp. in my hips and back. I've definitely noticed a difference going from 8 to 10.
I had to increase slowly, though. I got headaches from 6 to 8 and again from 8 to 10. At first they were crushing headaches, esp. 8 to 10, but I alternated days, which made it better, and then they stopped.