EHEIM Jager TruTemp Submersible Heaters

A long-established glass heater with an adjustable thermostat that can be recalibrated, which is a large part of why aquarists keep coming back to the line.

Key features

• Adjustable thermostat with a clearly marked dial, plus a calibration adjustment if the setting ever drifts from your thermometer
• Fully submersible, so it can be laid horizontally low in the tank where the flow is strongest
• Indicator lamp shows when the heater is drawing power
• Suction cup mounts and a generous cable length
• Several wattages available — match wattage to tank volume, or ask staff and we will size it

Widely used in both fresh and salt water. As with any glass heater, keep it fully submerged, mount it where water is moving, and unplug it before a water change so it cannot run dry. The rest of the brand is in Eheim.