Did my fish die from low salinity?

[Glowurm]

Sump yes, skimmer no. I think it's likely that I also had oxygen issues but I'm now several days in with the return jets facing the surface and the powerhead now running, I would think that's enough aeration wouldn't you? Plus the "waterfall" of the overflow line into the filter socks. With those changes, there's no change in the remaining fish's behavior.

Previously no, now, probably...