Nice job with all the tweaks, and glad it's quieter. I think at one point you were concerned about the eels getting stuck, and perhaps a low profile strainer?
I find that acrylic eventually starts to bend with heat from lighting and what not, but doesnt look like you have a need for lids now. I wanted to cover my internal overflow as well and used marine board. They have various thickness and can cut to size.
I did still put lids on the tank to keep my eels from jumping and to keep the water from evaporating too much.