Jamie - I am new to the shrimp hobby, but I have CRS as well in a 20gal, and I have noticed the exact same thing. At first, I thought it was after the molt, but have realized that it is before the molt that the males run around lifting the female's tail up by his head. Funny to have found this thread because I came on this morning to see if I could find out if it were just the males dancing around or if the females joined into the dance as well.... I have pinpointed which female is, as you suggest, apparently getting ready to molt because several of the others (presumably males) are doing this exact thing to her to the point that she is trying to hide from them. In fact, some of the males will run around lifting females until they figure out exactly which one is the one, and then they chase her relentlessly. Great observation and fun to learn about.