First viv!

Wallace is probably correct, though there is likely also a good amount dead bacteria in that layer. Still water betta setups will develop this harmless layer, the only other thing it really could be would be a protein layer but without decaying organics like food or fish I really doubt it's that. Water changes should solve the problem.

As far as fish you will have limited choices without water movement and filtration. My personal thought for a tank like this had always been the tiny sparkling gourami as they have labyrinth organs which allow them to breath from the surface. A betta could live in there if there is enough space but it's hard to tell scale. A betta, I would guess could pose a threat to the frogs. I have seen them attack african clawed frogs, by biting the frogs back legs.

The viv has a cool look to it, good luck.

Thank you for the replies!

Although now I'm pretty confused. Some of you are saying that there's not enough land area for the frogs. I thought the frogs liked a lot of vertical area?
This is an Exo-Terra 18x18x24 with a false bottom. So the water is much more than what is showing in the pond (under the false bottom). And the right side rear rock is a waterfall, so that should aerate the water plenty. Does that change what/if fish could be included?

I'll include another angle of the viv. If you guys still think it needs more land for the frogs, then so be it. After all, it's for them! (I can look at fish elsewhere! )

Also, if you notice, I'm getting brown edges on my black rabbit's foot fern. Do they NOT like to be misted? Is it getting TOO much light? Too little water? Any thoughts?

Thanks again everyone!