personally, I just use gravel and *maybe* cover with a thin layer of long fiber sphagnum moss (moss used in orchid pots). This way you dont have to worry about the substrate falling through the gravel, it's much cheaper and most vivarium plants will do just fine in gravel only as they will help remove the nitrogen build up in the drainage water. The moss merely serves as a buffer which keeps the pH where you need it and also improves the appearance of the viv (I've had the moss come back to life and it looks great!!). Another gravel cover could be oak and magnolia leaves. Frogs love leaf litter as it gives them a sense of security knowing they have a place to quickly retreat if danger should arise. The leaves also serve as nutrients for the plants and harbor springtails. I probably should use leaf litter more in my tanks, but for now I'm happy with sphagnum moss.
-Bill J.
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2.2.6 D. azureus
1.2.24 D. ventrimaculatus 'yellow'
1.1 D. tinctorius 'cobalt' (one subadult)
0.0.3 D. tinctorius 'patricia'
1.1 D. auratus 'blue'
0.2 P. aurotaenia