It has a minimum water level because it is made to be submersible, and would overheat otherwise. The condensation might go away after heating the tank for a day. Right now it's some fogging because the temperature inside the heater is higher as the water, and this causes water vapor in the air inside the heater to condensate on the colder areas like it does on the mirror in the bathroom when you take a shower. If it is still there monday you might want to contact the seller in case they want to replace it.