Might be too late, but the way I did my dart frog tank is with a false bottom made of egg crate and made it like an inch or so smaller than the bottom of the tank all the way around. We built a top and 4 sides and held it together with zip ties, then covered the whole thing with fiberglass screen and used zip ties to hold that on too. We cut out just enough to allow a piece of tubing to go through the egg crate and fiberglass at the point we wanted the water feature, then attached the pump from the underside.
Once it was in the tank, we filled in around the sides with pea gravel and covered the top with ABG substrate. The water feature is a piece of cork bark turned concave-side up with a hole drilled into it and another smaller piece of cork bark over top of the outlet to baffle it. The water collects in the curve of the cork bark. I put some java moss on it and it's growing nicely.
This is an old pic, I've changed it a bit since this was taken, but you can get the idea on the water feature.
When I can no more stir my soul to move, and life is but the ashes of a fire
When I can but remember that my heart once used to live and love, long and aspire
Oh, be thou then the first, the one thou art, be thou the calling, before all answering love
And in me wake hope, fear, boundless desire.