Disaster has struck yet again. Second background was done, I cured the concrete for a week, air cured the epoxy a week, and had it in the tank and with water for a week. I did two 80% changes, the second being last night before I added my fish. I woke up this morning to all ten neon dwarf rainbowfish and two snails dead. My striped Raphael was still alive, so I immediately pulled him out and have him floating in a bag in my 30 hex for the moment.
So frustrating! I don't know if it was something from the background that killed them, or the fact I had to adjust my heater (in-line) last night cause the tank was sitting at 72, I adjusted the heater to 78 before I went to sleep. I don't think it was the temp change, as it wasn't a huge difference. They had been in the tank at the most 10 hours, and they were moved in right after the 80% change.
If its the background, and its something I can't fix the tank is toast, there is no way in hell to remove the background back out without tearing the whole thing apart.