Did you drill a 20L for the fuge and just run the full size 20L for it? I’m thinking of doing the same thing. Bare bottom it looks like?
My fuge(which is off line at the moment) is a 20L drilled up to the black plastic trim. I'm done with sand in the fuge. It's too much of a pain for the little benefit of the amount of sand a 20L can provide. In order for the sand to be any benefit, it has to be 6" or more in the fuge. With a drilled 20L, that leaves little room for macro algae.
I took the fuge out of the system to clean in late fall. Haven't got a chance to put it back.