hi can anybody help

That would be my guess if it were just shrimp, but it is kind of acclimate crabs and snails wrong. Temp is the only one that affects most species as they are mostly from intertidal areas. Considering all his animals died I am guessing copper or stray voltage. EDIT: I am also assuming his acclimation technique can't be too far off considering he got at least four fish in there.

How do you know all of your animals were dead? You said they died within 3 hours? It is not unusual for snails to remain closed up in their shells for well over that. "Ceriths may go dormant for up to 3 days." - from the reefcleaners.org acclimation page.