Linda,
My Exo-Terra has a combination of Hydroton and PrimeAgra mixed underneath the Aussie gold, I did this only because I didn't have enough of each to provide the coverage that I needed,check out my gallery to see some pictures on how I assembled this project.

Ross,
I did as you suggested and turned the fan off and the humidity jumped up to 70% but don't I need air circulation for the health of the plants. I have Hydoton and PrimeAgra under the mix to help keep up the humidity.

Did you soak the Hydroton first?

I have a fan running in mine 24/7 with humidity up to 99%.

I have a fan running 24/7 INSIDE tank. The thru wall only runs 3 hours at night to exchange air. No, you don't need through wall all the time. I would consider adding a second 12 volt fan inside tank for air movement (not air exchange).

Yes, I soaked the Hydroton before I put it in. The top of the Exo-terra is open with a screen on top, the fan I have just blows down thru the screen in one corner, should I close in the top and mount a small fan inside?

Try it and see. Don't close completely. Just keep sliding a glass top across till you see max humidity. Try to leave a couple inches open. You don't need the screen - it's for frogs, etc. Screen cuts down the light also.

An update on my terrarium.
Ross I removed the screen and the light levels went up, but I have not yet closed the top, I did turn off the fan blowing directly into it and left air circulation up to the ceiling fan. The humidity is in the 50's at night and as high as 80% during the day. Today I plan on going to the glass shop to get a piece of glass to cover the top.
I have partialy planted it, here are the current pictures.
Laelia reginae (upper left far back) (2600 foot candles)
Aerangis luteo-alba (upper left) (1982 fc)
Haraella odorata (on right in front of water fall) (211 fc)
Masdevallia noid (front left corner) (220 fc)
Neofinetia falcata (back lower left) (320 fc)
Dendrobium aberrans (back to right of Neo.) (345 fc)
Maxillaria uncata (back, left of water fall) (345 fc)
I hope I'm providing the correct light levels.

Beautiful set-up! You did a great job! :biggrin: I did want to add that the den you have would probably do better a little higher. I just bought one from Andys and they listed it's preferred light levels at 2500fc. I know Ross has one so maybe he will chime in. :lol: How did you attach your quickie project orchid to the backing? Just curious!

I think if it were mine I would rearrange a few. The D. aberrans wants really high light. Mine is approx 6-7" below 4 t5 tubes (1600 FCs) Same with Maxillaria. Neofinetia likes full sun. Mine is up in the grow window where it gets dryer air and full sun. Aerangis can be further from lights (say 500-1000 FCs) Don't know on the Masdevallia, don't have any. I am basing my observations on nearly a year of growth under 48" t5 lights which produce 20,000 lumens (approx 1600 Foot-candles). Anything higher than that goes upstairs in a south-facing bay window where they get full sun most of the day.

BTW, glad you removed screen. You'll be happier with higher light. Glass can be "single-stregnth" picture frame glass. Just keep sliding it across top till you achieve the blend of fresh air to humidity that you are happy with. You may want to set venting fan on an applience timer to come on for a few hours at night to vent the tank of old gases, etc and just contribute a bit of fresh air. Mine runs 3 hours each night. I am sure humidity goes down during that time, but not too much. I run high 90% range during day, so I feel this gives plants a rest from too much moisture and maybe dries the rotting microbes out a bit? My tank maintains about 1/2" inch excess water in bottom and that probably off-sets the added dryness of the thru-wall fan.

If you are after plants for the bottom where light is really low, consider the "Jewell Orchids" like those Little Frog Farms sells. (Robe is a forum member) I have 5 in the very bottom of my tank and I had to move one to get less light because the leaves were burning. We're talking really low light here - maybe less than 200 foot-candles!

Thank you all so much for all the help and tips that I have received.
The quicky project is not truely mounted to the back, it is wedged in the fork of the Mansanita branch so that it can easily removed to be put outside in full sun during the day.

Ross I really appreaciate the time you give to all here and the advise you give. I am taking your advise and am rearrangeing a few of my orchids to make them more happy,and look for a few more to complete the set-up.

Thanks so much to all, for your input and suggestions
Mike