u/HolidayNo4132

I’m looking for ideas to block the horizontally oriented sump overflow at the bottom of the picture. The cardinal tetras have been dying getting into the sump this way. I don’t want to use sponge or cotton, as it wouldn’t look aesthetically pleasing. I was considering using an inert lattice, but I’m not sure how to fit it into the L-shaped design and keep it at the bottom. I’m seeking suggestions from fish tank engineers and other highly intelligent individuals who can provide innovative ideas.

Is the redness around gills sign of sickness? Both angelfish have this. Water parameters are all good and see no other signs of sickness in the discus fishes in the tank.