The odds of saving small finfish were marginal at best.
Shrimp may not be very bright, but they are not suicidal!
I am taken aback by the apparent aggressiveness of your Dwarf Cichlids.
What you are seeing in your substrate is analogous to what is happening in your bio-filters. It is fascinating stuff…
I think the whole tank is on track as far as operating, I just think there is something else going on… More on that tomorrow.
The chlorine forming chloramines is quite possible and fits with my sense that there are residual DOC in the tap water. Still activated charcoal and RO, then DI should remove pretty much everything.
So how is the water pressure?