Sounds to me it was the acclimation, 30 minutes is quite fast, best to drip them over an hour or better 1.5h,then check temp is correct, you need to make sure the shop water is near enough fully replaced with your tank water over a long period before adding to the tank? Just adding a little tank water to the bag a few times over 30 minutes is not going to get the salinity, ph and alk to match your tank, inverts need a slow acclimation,!fish are not as delicate.
No evidence of a pollutant killing the cuc.