Best to either juice your own Fuji apples, eat Fuji apples, and you can drink organic apple juice from the health food store or country store. Frozen concentrate has very little real juice in it.

You can also purchase Malic Acid or liquid Phosfood.

There's no risk. :) The stones will get smaller, softer, and even dissolve into chaffe. What often happens is people will eat a high-fat meal, do some bending and stretching, and end up expelling stones absolutely pain-free! It's way cool. :) I have yet to hear of anyone getting a stone stuck due to pre-treating and shrinking them.

Fresh pressed is best for drinking to soften stones. However, I use plain old bottled or concentrate to make the Epsom Salt drinks. Most of the time I'll mix fresh and bottled juice to save money. On my last flush this past weekend I mixed frozen apple juice with energized water, mostly because it was there. I had the best flush ever in terms of getting out large stones.