Dwarf zebras, and extremely small lionfish seem to be VERY sensitive to changes in pH or salinity. I never had the best of luck acclimating dwarf zebras ordered online either (alwayas dying during the first night), then my friend told me any lionfish under 1.5" and all zebra dwarfs and radiatas should be acclimated no less than a slow 8 hour drip. Since then I have successfully acclimated a dwarf zebra of about 1", a dwarf zebra of about 3", and a radiata lion of about 3/4". Alll are big, fat and happy over a year later!
Jon