In a ten gallon, you may be able to place some of the smaller darts, but beware, just because they are small doesn't mean they don't need alot of room. If you really want to breed things, invest in larger tanks and use the small ones as nursery tanks. That's what I would do anyways.
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I think my frog owns a megaphone....

White's tree frogs : 1:1
Mantella viridis : 1:3