My 100g makes my small room humid and smelly, if i put a glass top over it will this prevent that? will this prevent my fish from getting enough oxygen, if so how can i get them enough oxygen and prevent the humidity?
I run 1 dehumidifier during the winter in my basement and two during the summer. It keeps the room more pleasant and keeps the smell down. I got one of them almost brand new from a garage sale for $10. Check Craigslist.org and see if you can pick one up in your area for cheap.
A lid will definitely help keep the evaporation down, as far as getting oxygen in your water you just have to worry about breaking the surface tension of the water. Do you use a hang on filter? If so you should have enough of a gap around the lid for the filter and that will be fine. The same goes for the hoses from a canister filter. You could spend a few bucks on an air pump and bubble bar too, that will bring in air from the outside as well.
the dehumidifier would work for humidity but i dunno about the fishy smell. i would say get a lid and put an aerator in the tank for plenty of surface agitation and IMO you should be fine.
Cover that tank!!! you can do some real damage to your room. As everybody else said: a filter should provide plenty of O2. if you are worried about it, buy and air pump and stone.
Cover the tank, I have always kept mine covered. If it is still humid, get a dehumidifier. Don't waste your money on chemical dehumidifiers, spend the cash and get an electric compressor/condenser unit.
For my top I use my local glass company, just measure what size you need and they will cut it. I would suggest a thickness of 1/4", I have 1/8 tops on one of my 55g and it just seem to thin, I always worried I'm going to break them.