We've been very happy with the floors, and the easy cleanup. There have been spots of efflorescence appear, however. This had come up through the floors, and was trapped under the sealer.
I did lots of research on the internet, and did not find much addressing this particular issue. I was able to gather enough to experiment with Xylol, also called Xylene, I believe.

I tested this in a few small areas, and it worked well. It was able to dissolve the remaining sealer, and clean the efflorescence at the same time. I've gone on to clean most of the floor with Xylol, and re-sealed it. It looks as good as new.

As these floors gain in popularity, more people will be having this problem. Hopefully some will search here, or if you're planning such a floor, file this away for future use.

As always, test a small area of your floor first to see if it works for you.

Our concrete guy told us today that he couldn't in good conscience acid stain our floor (in a basement dig out) since the moisture level was too high and the entire floor would turn white after five or six years. So we're just going to wax and polish the gray concrete. I'm coming to terms with it.