Growing problems

[Toadchick]

So I've had my 29 gal viv for about a year now: 2 inches of hydroton, 1.5 inch of soil (coconut coir, organic potting soil), thin layer of banana leaf litter.

I keep a very chubby Hyla squirella and a couple Eleuthrodactylus planirostris (which breed on occasion). Small crickets are chucked in about once a week, and I mist the tank every couple of days in the dry season (down here in Florida, that is October - April) and then as often as it rains in the wet season (read: daily x 2) This is to mimic conditions outside, where the frogs were caught.

The problem being that I have pothos, arrowhead vine, and bromeliad in there currently, and the arrowhead vine is just not doing well, plus every time I try to introduce a fern into the tank, it dies. The lighting is a single strip 20 watt that came with the tank. Is this too dark or too bright for the ferns? Or is it the humidity or soil that is killing them?