Leca as substrate for terrarium -- algae?

[estación seca]

A half inch of water in the bottom would give the same humidity as 2.5". Do you need more than one layer of LECA below the level of your drain? Evaporation and humidity are proportional to the surface area, not the water volume. Having a very shallow LECA layer would give you more growing volume above, which is what every terrarist wishes they had more of. Raising humidity in terraria is generally not a problem.

[MJG]

You're making me revisit this, which is a good thing. I came up with my plan after reading about others' vivarium builds on blogs and websites. NEHERP is also a great resource for vivarium builds. They have some instructional articles online that are helpful.

It seems that for the bottom wet layer people either use raised eggcrate with freestanding water underneath or a layer of leca. NEHERP recommends leca. They say that the other purpose of this layer, besides humidity, is to allow builup of beneficial bacteria. Leca provides more surface area for that than does eggcrate.

In revisiting NEHERP's articles just now, they recommend 3" total of leca, with the drain placed 1/4 to 1/2 the way up. But they say to vary that with the size of the vivarium. I think it was the large size of my enclosure (plus my fear of drilling glass so close to the bottom of the tank) that led me to my leca layer sizes of 2.5" wet plus 1.5" dry. I don't mind losing an inch or so of growing height in a 36" tall vivarium.

I could cut the wet layer back to 1.5", and perhaps I should, but I still worry about algae control. Also, you are certainly right about evaporation being proportional to surface area. I am clueless, though, about how much evaporation will happen every day. I'm going to be running exhaust fans that suck air out of the enclosure.