I've used the 8 gallon plastic totes as QT and grow out tanks in the past. A simple sponge filter, and you'll be fine.
For neos, I'd skip the substrate and put down mats of moss. Much easier to clean long term, especially when you have babies everywhere. Just move the moss to one side, clean the bare bottom with an airline tube siphon, and repeat on the other side.
For caridinas, buffering substrate is almost always recommended, but I doubt you'd want to put nice shrimp in an ugly container...
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