My froggies are very tiny and almost entirely terrestrial, and my fish are all very fast (and mostly wild-caught). I don't think the fish and frogs are even aware of each other. Ignorance is bliss, and they all live together in harmony. I'll try to get a video of the whole thing one of these days. It's a rather nice setup for both worlds, if I may say so.
I discovered a little cave in the moss beside the waterfall where Ago has been hiding out. So I took a walk and found some rounded bits of cottonwood bark which will make tiny caves. Hopefully this will make them happier and less inclined to vanish and worry me.