The frequency of how often a filter cartridge should be changed will vary according to how much waste and free-floating algae is in the fish tank. The general recommendation is to change the filter cartridge once per month.
Aquariums containing live plants should receive 10-12 hours of high-quality light per day. Tanks with artificial décor only need 5 to 8 hours per day. Hours of light should be the same each day as fish rely on a daily rhythm for their activity and proper health. Use a timer to provide a consistent day/night cycle and never leave the aquarium light on all the time.
No, simply seeing condensation inside your Aqueon Glass Adjustable Heater does not that it is broken or defective.
Check that the heater is working properly by using a thermometer with your fish tank. (also make sure that the water is the right temperature for the type of fish that you have inside your fish tank)
The reason you may see condensation is because humidity was in the air and trapped inside the tube when it was manufactured and sealed. Your heater is still able to perform properly with this condensation.