TempTec Advanced Quartz Aquarium Heater Quartz Silica Tube - Maximum strength quartz silica tube is shatter resistant & more durable than conventional glass heaters Accurate Control - Accurate thermal control achieved via easy set thermostat for precise adjustments Gravel Guard - Gravel guard tube cap & advanced mountain bracket included. Mounts both vertical or horizontal positions Active Indicator -Blue On/Off LED indicator & temp setting is easily viewed from multiple angles. Submersible - Completely submersible in both freshwater and marine systems.