Ventilation problem

[calivivarium]

Hi guys, this is my first post here but i have been reading when I can for a few weeks. I am glad that I found this nifty place to gather new information about vivariums. I currently have a problem in my first vivarium, I believe its a ventilation/humidity problem.

I have recently purchased a 20gal high vivarium(paludarium may be proper term for it.. I can post pics this evening) with aprox 5gal of water on the bottom, eco-earth on HF background, and several pieces of wood. The plants include two types of micro orchids(which I thought I had stabalized, it appears they now need help), "dragonscale fern," moss, a wandering jew, and two kinds of vines. Seeing as all of these guys need a humid environment, the tank came with a piece of glass to cover the top and keep the humidity in.

i guess all of this is to say that.. is leaving the glass on(except for a short period of time morning/night to let air cycle) more harmful than beneficial? Would I be able to achieve proper humidity levels with keeping 1/2 the top covered and misting more(quantity wise, I am not home often from 8am - 6 or 8pm)? My orchids appear to not be able to dry out for long enough periods of time, and my wandering jew is suffering from fungus as well.

I have no soil, so personally I am wondering if the plants(again, i did not set this up myself) themselves are the problem. The plants are all growing either in moss/eco earth or simply attached to the background. Maybe this is not a suitable habitat for the plants I have in the tank? Any website/criticism/ideas/comments are much appreciated, and once again I can post pics when I return home this evening. Meanwhile, I will continue researching ventilation on this site and others...
Thanks,
Sean

[Red Eye]

Try some sort of a fan... air movement might fix your problem