I assume you mixed your salt for 24 hours and matched ph/temp/sg
to the main. If not then the resulting shock to the system could likely be the culprit. How large was the pwc
? Was there a power outage while gone?
Lights out for 2 days wouldn't have killed off your SPS IMO
. Corals go for days in the wild without light during inclement weather.
How are your water parameters now like nh3