I have a very old (10+ yrs) generic no-name heater which I decomissioned from aquarium duties and now use it in my hydroponics reservoir. There is algea on the inside of it, a bunch of oxide dust in the bottom from the heating element corroding, its discolored from heat, has crusty salt build-up on the outside of it and the rubber sealing the top is so perished that it crumbles in your hand! But for some strange reason it keeps working!? LOL!