Besides letting the tank mature, you've got to let the shrimps acclimatise properly before adding them to the tank. After letting them get used to the tank temperature, add a little of your tank water into the bag, leave for awhile, and repeat again.
If you kwai kwai, maybe 30mins for them to get used to the new water conditions. Do a search here about acclimatising shrimps, there'll be better suggestions from the others.