I find that the heat needs to come from the bottom, and seeds/seedlings will go crazy. Think about a nice spring day in the garden and working in the nice warm soil with your hands. Better than sitting at the computer with cold feet any day.....The plants do not like cold feet.

Now, as far as mold, the spores are coming from somewhere...sterilize your soil before you use it by baking in a container in the oven at 350 degrees for an hour. Use chlorinated water at first fresh from the tap, it will not hurt seedlings at all, in fact I believe it reduces issues with mold and bacteria at this vulnerable stage. Keep them in a humidity dome with a heating pad under it until 3" tall. They make special pads for this, cost about $20