a lil school of red tail barracudas cruising around the top middle area would be cool! or yellow, or hujeta
hujeta gar are very pretty and stay at the top at least as I've seen
a ropefish would round out your polypteridae collection nicely, and my friends tends to wrap himself around plants and stuff in the middle and top most of the time
I've recently seen some videos of fahaka puffers being commed w/ bichir, idk if you want to take that kind of risk though haha
there are some neat mormyrids out there that may interest you too
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