Are super glue and cracked glass on submersible fish tank heaters compatible?
Don’t do it! Fried fish and possibly dead you are distinct possibilities. Bite the bullet and buy a new heater, if you’re lucky a big pet shop may have a repair kit with a new tube and correct sealant. Even then I’d be leary unles you have experience and most submersible heaters are pressurized to help keep the water out. At the bottom of a two foot deep tank the pressure on the tube and the holes for the connections is about one foot per square inch more than it is at the top.
