Eheim Jager 300W Aquarium Heater

The Eheim Jager 300W Submersible Aquarium Heater with Thermo Control is the powerhouse of the Jager line, built to warm large aquariums of roughly 159–264 gallons with rock-solid German precision. Fully submersible with the calibratable TruTemp dial (65–93°F / 18–34°C), shatterproof glass, and automatic dry-run shutoff, it keeps big tropical and marine tanks at a steady, safe temperature.

Why aquarists trust the Jager

• 300 watts of reliable heat: Built for large aquariums in the 159–264 gallon range — the top of the Jäger lineup
• Precise TruTemp dial: Adjustable from 65–93°F (18–34°C) with a calibratable dial for spot-on accuracy
• Fully submersible: Mount it horizontally or vertically, freshwater or saltwater
• Shatterproof glass: Lab-grade, durable construction
• Thermo Safety Control: Automatic shutoff protects against accidental dry running

Setup & safety tips

• Place the heater near good water flow (by a filter outlet) so heat spreads evenly.
• After plugging in or before unplugging, wait ~15 minutes for the glass to adjust to water temperature.
• Always verify the actual tank temperature with a separate thermometer.

Not sure on sizing? Looking at the larger Jagers? Compare the 200W and 250W. Browse all aquarium heaters or the full Eheim equipment lineup.

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