Looks like a geo tank to me. Maybe a school of rainbows or denison barbs for upper water activity or a couple dozen tetras if you want to stay more more biotopish.
Its such a hard choice I'm with you on that one that's why I've got so many tanks set up
I'm sure whatever you choose will look great as plenty of thought has gone into it , it does shout geo tank to me though , or have you thought about severums ? Ive never kept them myself but they would look good in a community in your tank , Just another ball for you to juggle hahaha
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