Re: 12x12x18 - Help me visualize
I grow Pilea mollis/involucrata in crested gecko vivs. I've tried it in dart vivs, but it melts (too wet, I think).
The other two plants you mentioned strike me as way too large for a 12 x 12 x 18. They would just fill the viv and squash out through the seams.
As an example, I think a big plant for a viv that size is a Neo that grows 5 or so inches across; a plant that big really is hard to deal with.
Not sure what frogs are going in there, but it matters: some frogs like/need lots of broms, some like a few large-leafed plants...
"People are like plants, they grow toward the light."
- Hope Jahren