It is possible the Lemon Tetra
and angelfish occur together, the former occurs in the Rio Tapajos basin (a southern tributary of the Amazon in Brazil) and the latter in the Amazon basin (including the Amazon itself in places) though primarily in norther tributaries I suspect. Still, suitable together. The other Hyphessobrycon species also make good tankmates for angels, being disk-shaped. The rosy clade is especially good, fish like the Roberts Tetra
, Rosy Tetra
[these add a nice reddish colour to the tank], Black Phantom Tetra
and Red Phantom Tetra
, and others. Not Serpae Tetra
though, will nip fins.
A comment on the light hanging from the ceiling. If there is any visible space between the fixture and the tank, the light will shine in your eyes and not be conducive to viewing. For this reason, unless the light is somehow enclosed, having the fixture directly on the tank frame is best. All you need to do is select a single tube T8 fixture, or even a dual tube, but only T8; T5 is far too bright. Then floating plants. Water Sprite
will easily cover the surface, I have done it, and the tank below is very dark. You can thin it to your liking. Some Brazilian Pennywort
planted in the rear corners would frame the scene nicely, and be authentic, replicating hanging vines. This plant complements angelfish nicely.
The 75g should work, at 4 feet length. The sand substrate will be thin, only an inch or less, more a sprinkling. Playsand from Home Depot is ideal, it is very close to the colour of the sand in the Rio Negro basin so very authentic for angels. Some corydoras would be nice too. You will have wild angels, so they need warmth, 80-82F minimum. Your tetra will have to manage with that, so check the temp ranges in the profiles. Corydoras sterbai
do fine at these temps, most other corys would burn out.