If the smaller tank has had fish in it for a while, it has already cycled, so I would put any fish you want to keep in that.
Do you have a test kit? To truly understand and properly cycle your tank you'll absolutely need one, preferably an API freshwater master test kit.
Got a question about loaches? Ask me!
Loach count: 21
Baby fish count: 700+ (shelldwellers, gbr, angelfish)