So far only partial parameters have been posted unless I missed something. Alk and salinity numbers? How often water changes? Using RODI? Any ICP test to look at everything? I Agee with some of the other posts. Overnight deaths are often 02 related or poor water quality. Disease can enter the tank via different routes but you would probably note some distress signs before death.
What is your sump turnover rate gph? Are you getting enough dwell time in the sump?
What is your sump turnover rate gph? Are you getting enough dwell time in the sump?