terrarium conundrum

[missclick]

Hello!

I have 3 full grown whites tree frogs in a 18x18x24 zoo med terrarium.
Problem: keeping it clean, too much water.

I have:
-all fish gravel substrate w/ 2 inches of water
-filter
- sticks/fake plants

I want to:
-Have only a corner of water and the rest be substrate
-waterfall?
-live plants

-- how do i keep the substrate out of the water?
-- what lights/dirt etc do I use to keep plants alive?

My current water pump cannot keep all the water clean.
I'm considering making a background out of the expanding foam, is it incredibly difficult? Is there frog-safe paint?
Contemplating the egg crate false bottom/hydroballs/mesh/substrate route.
I feel bad if my frogs eat substrate and moss...
All water right now makes it hard to feed crickets without them drowning.

Will silicone rubber attach wood and plants to glass?

Is there an easier way to make the ideal house for whites tree frogs?

Sorry this is kind of random, I just wrote all my ideas down as I went. I need help finding a way to incorporate more land into the terrarium while still being clean and functional and not bank breaking.

thanks!