Crazy.I took out chaeto and changed GFO about 4 days before leaving. I did rinse GFO, not a ton - just one strain through the media cartridge.
I don’t think I added chlorinated water. It’s the same rodi system I’ve been using and I added the same water to my frag tank and I don’t have any losses there.
I do have nems but none got into power head. No cucumbers, only 2 urchins.
Unfortunately no recordings.
Any other things you did to the tank before leaving? Last second pipe tweak it Kalk / doser change?
Any other last second things you did in the house before leaving? Cleaning products, mess with ventilation?
You said your family told you that things were bad. There someone still at the house? If so, and all other things were even, that'd be suspicious to me. Leave town, someone does something innocuous in the house trying to kill some bugs, or help the tank, or ... What were you doing to feed while gone?