Ghost shrimp don't seem to do as well in soft water. Not sure why, entirely based on personal experience, but my ghost shrimp have always done much better in lightly brackish tanks--not sure if it's the salt, or a trace mineral from the marine mix, or the buffers in the marine mix.
There are some truly stunning algae eating FW shrimp--but be prepared to pay a bit more. Also, be careful about selecting tankmates. Many fish eat crunchy things in the wild, and will not realize that you didn't intend the $12 Cherry Shrimp to be a nice snack. Also, some crustaceans are not good tankmates for fish--crayfish will eat anything they can catch, even that expensive pleco.