I'm in the process of creating my first dart frog terrarium... it's a project I'm completing over the course of the year so that I don't rush anything to cause imperfections, and that I can create the terrarium to the best of my ability. Right now I'm starting to create the false bottom/drainage layer and while I see that everyone seems to recommend using LECA, I can't find anything that tells me exactly what it does to benefit a drainage layer.

My questions pretty much come down to:

1) What is the function of LECA?
2) Will using it require periodic replacement or will it last through the life of terrarium?