Tetra Water Wonders 1.5 Gallon Tank fog?

Is there a way to keep this tank from getting foggy where there's no water? You have to stop filling up the tank about 1 or 2 inches from the surface because of the filter but the lid is clear too. I got the Tetra 2-10 gal heater for it and it works great but I think that might be the reason why my tank is fogging up. It fogged up a little before I got the heater because my room was extremely cold, but it looks more fogged up now. Is there anyway to keep it from fogging or do I have to deal with it? I'm planning on getting a 10 or 20 gal next month for my betta, but the fog is bugging me because it makes the tank look unattractive even though it's pretty cool modern looking.