Neem oil.
I pretty much believe neem oil should be in every grow room. Its totally non harmful, and is effective at treated just about everything. Any time I'm suspicious about fungus, or bugs being around I don't even think to spray it. If nothing else it makes my leafs perdy!
Dyna-Grow neem oil is pretty cheap, just mix it up with some NON-antibacterial soap put it in a sprayer, and spray all the leaf surfaces.
If your suspicious about fungus there a couple of factors worth investigating though. Normally fungus will only develop in environments with high high humidity. So if your humidity is above 50% it is a possibility. Also air circulation will set fungus back a little bit. Do you have a fan blowing on your plants?