Help Stocking A 55 Gallon

[rockdon]

HEY everbody my neighbors just lost their entire cold water stock to ick and i mentioned tropicals to them looks like they re probably gonna get some.
the tank is 55 gallons and is (?octogonalishly?) shaped its got two bubble rocks in it as well as a couple of hiding places and flat rocks no live plants though just a couple plastic

dimensions are 23in long 23in wide and two foot deep
any help is apriciated!

 

[Oscar Betta]

You could do a discus tank, but it's for more advanced fish keepers, IDK how advanced they are.