I have successfully kept Amano shrimp (Caridinia japonica) for about 5 1/2 months now. I have read quite a lot about them in this time.
They are very sensitive to water quality ESPECIALLY HEAVY METALS. Is it possible that something in the Flourish is too much for them?
Also are you sure they died? - Did you find bodies?
Fish as small as Glowlight Tetra have taken a chunk out of a shrimp tail, wouldn't take a much bigger fish to kill one. However the shrimp have good defenses and can be quite aggressive themselves.
Have you ever found exo-skeletons (shed skins)? These are a good sign that your shrimp accept their water conditions. Never finding any is not good at all, mine were all shedding in the 1st week.
The shrimp who survived may not be the only one, just the only one brave enough to come out. What fish are in there? How big is the tank etc?
I might never find my way back to this thread so I hope what ive said gives you something to go on. If you need any help at all with shrimpy stuff feel free to email me anytime mat AT happyhardcore.dj
Good luck, Matt