Agree with the others about improper acclimation. You need to check Salinity/sG
and Ph and drip slowly till the water from the LFS
matches your tank.
I use a tupperware bucket to do my acclimations, dump bag with fish/invert into bowl and then start a drip line from the tank. I use a air line hose with a valve on the end to control the water flow. Check salinity and Ph after a hour and if they match i run another 30 min to be safe. If not the same dump so water out of the bowl and keep going. If fish and inverts are in different systems at the LFS
do not mix them at acclimation, you need to do them in different bowls.