Schego PTC Titanium Aquarium HeaterImportant Information Please Read This is an unregulated heating element. It MUST be operated with a reliable, external temperature controller (sold separately). The controller will switch the heater on and off based on the aquarium's water temperature, while the heater's internal PTC technology provides the critical redundant safety layer. What is PTC Technology? PTC stands for "Positive Temperature Coefficient." Instead of a simple resistance wire,