In response to the remarks made by the two Marks on Fluo-3:
 
The molecular probes catalogue (1992-1994) page 116 states
that Calcium Green indicators are about 5 times brighter than fluo-3
at high Ca2+ levels and BLEACH at a significantly slower rate.
 
I have used both types of indicators in crayfish motor
 nerve terminals and found that fluo-3 bleached so rapidly
 that I could not use it, whereas Calcium green
 worked wonderfully
 (Cooper et al., J. Neurosci. 15:4209-4222, 1995).