This was a random juvenile cichlid tank I had like 15 years ago. Yes a juvie distichodus sexifasciatus (the only african fish I ever kept.
4 juvie festae
4 juvie hatiensis
4 juvie crenicichla sveni
1 L199
1 albino BN
Plants were
rotala rotundifolia
java fern
valisneria
ludwigia repens
a moss wall with java moss
No C02, but it had very high T8 lighting (this was way before LED lights were a thing in the hobby)
Yes. Southern California water is basically liquid sandstone, but I ran the water for this tank through some type of showerhead filtration system. Not sure if it softened anything at all but it did filter out chlorine somehow.
I would not do duckweed. You could add water lettuce or frogbit if the surface movement is not to rambunctious. Water lettuce and frog bit won't live under water but duckweed will and once introduced to a tank all it takes is one little piece and it will be the gift that keeps on giving.