Pretty sure this is NOT related to this incident at all (sorry for your loss) but just saw that your open sump is near your washer & dryer. Since I’m the only one that does the laundry at my house, it raised a few possible red flags you may not have considered if you aren’t the primary laundry guy.
1. If you are using any powdered detergents or additives (Oxiclean, Borax) they are fine grained, easily spilled and get everywhere.
2. Dryers make LOTS of lint. I clean out the dryer filter after each load and put it right in the trash bin. Somehow I still end up with “lint bunnies” all over the laundry room.
3. I’m sure you aren’t using aerosol air fresheners anywhere near your main DT, but is anyone using fabric stain remover sprays to pretreat laundry? I have no idea exactly what is in them, but it can’t be anything good for fish.
May want to consider a cover for the sump or maybe find a way to partition that section off with something as simple as the plastic sheeting you use to keep drywall dust from spreading.