I'd say the Colosan (or Oxypowder ) would be fine during a Juice Fast. Don't set a number of days, but rather take it one day at a time.
I've done a 21-day Juice Fast here recently and felt Great. I took Oxypowder during mine. I need to do another one. I like the following Juices....Wheatgrass, Carrot, Celery, and Watermelon Rind. I considered Watermelon as part of the Juice Fast.
Good Luck.....WY