You should have drip acclimated everything. I usually will drip acclimate anything I put into my tank for about 1 - 2 hours depending on what it is. Fish can sometimes be acclimated for a little less but I wouldnt go any less then about an hour or so. Fish dont necessarily die right away and can take sometimes days to show any signs of stress and/or death. Also if your tank is brand new there could be cycle issues or water chemistry issues. You should add things slowly to your tank.
Also for fish the best thing to do is set up a quarantine tank and over the span of a week or 2 slowly acclimate them to your tank water by doing water changes. This is also a prime opportunity to watch for any signs of disease or stress and try and correct it before introducing the fish to your main tank. A small 10-20 gallon tank and bio filter usually can do the trick. The investment and time is well worth it IMO.
Leemar 120g, 2 AI SOL blues, 2MP40s, custom sump, reef octopus XP2000, EcoBak Pellets, Koralian calcium reactor.