I have a 33 gallon for my WTF and his humidity doesn't drop below 45% is I stay on top of it. Sometimes I only have to mist once every two or three days. Given, I live in southern California and it is much more humid here because I'm right by the beach.

I have one large bromeliad, cutting of a snake plant in two places and two separate little bamboos in his tank. Also I have jungle bed on top of screening and hydro balls, moss on top of all that and some leaf litter covering parts of the moss. This keeps the humidity higher that it used to be with just the plantation soil substrate.

The tips given here are totally correct and helpful, so if you try to follow these you should be alright.