I wish they would grow in one of my set ups! I think they look really good! but to answer your question, no, I dont know of anything that will kill off mushrooms/fungus, Im sure that if you do find something it will prob kill any little critters you might have too =( I know theres a little in that lives in soil, it eats up dead and decaying matter, I think their called springflies? not to sure though?

The correct name is Springtails, here a link =)
http://www.uky.edu/Ag/Entomology/entfacts/trees/ef420.htm

"Since then, a great number have come up, and they're inching closer to my plants."

Well your plants obviously don't mind them. The mushrooms are merely the fruiting/reproductive bodies. The fungus has already infiltrated all of the soil including that amongst the plants' roots. If your plants were going to be harmed, it would have already happened.

Hi- We're terrarium neophytes and I'm hoping some of you have experience that could help us. We're in the process of setting up a terrarium for poison dart frogs. We haven't gotten the frogs yet. We have set up the habitat though, and in less than a week we have a fungus problem. We'd like to know 1) is this fungus likely to harm our future frogs and 2) what can we do about it? We know about springtails and will try them, but is there anything else we can do? We are also going to get a little laptop fan to help with airflow (we have a waterfall and mister, so hopefully that won't cause a problem witht he humidity). If we need to clean out and start all over again, how do we prevent this from happening in the future (the spores are now unlikely to be removable from the terrarium). Our substrate is coconut fiber with a layer of purchased mosses on top. The fungus is a white spiderwebby thing that is in the coconut, but sending fruiting bodies up through the mosses. There are a few plants in there, but we haven't finished adding those yet. The plants, as yet, seem to be unaffected. The jury is still out on whether or not the mosses are succumbing to their housemate.

Any tips and suggestions would be most welcome! Thanks a lot!!

Susan

I dont know much about fungus, but I know I dont have any problems with it when I use fans, I would add the fan and wait a bit, keeping the temp and humidity in check, then if the fungus doesnt go away in about a week or so, Id tear it down and build it back up, this shouldnt be a problem as it seems that you have a simple set up, no insults intended as a lot of the time I wish I had bilt a simple set up! LOL! let us know how things work out =)

Susan, don't you worry about no mushrooms. They're just a sign that your vivarium is functioning as it should.