Eheim Jager 200W Aquarium Heater

The Eheim Jager 200W is a glass thermostat heater made in Germany. You set the temperature on the dial, and the heater switches on and off to hold the water there. At 16 inches long, it’s sized to stand in a mid-size tank, and the 200W rating gives it enough output for a typical community or reef aquarium in a home that stays reasonably warm.

Sizing the wattage

A common starting point is around 3 to 5 watts per gallon, depending on how cool the room gets. By that guide, 200W suits tanks in roughly the 40 to 65 gallon range. In a cold basement or a big tank, use more wattage or split the heat between two heaters, so a single failure doesn’t leave the tank cold. In a small tank, 200W is more than it needs, and a stuck thermostat could overheat the water quickly.

Calibrate it before you trust the dial

The listing notes the heater may need to be calibrated before use, and that’s worth doing on day one. Here’s a simple routine:

• Put the heater in the tank and let it sit for about 30 minutes before plugging it in, so the glass matches the water temperature.
• Set the dial to your target and leave it for a day.
• Check the water with a separate thermometer. If the reading is off, follow Eheim’s instructions to bring the dial into line.

Placement

Mount it where water flows past, near the filter outflow or a powerhead, so warm water spreads instead of collecting in one corner. In a sump, put it in a section that keeps a constant water level. Unplug it before water changes and give it time to cool before lifting it out, since a hot glass heater can crack in cold water or air.

A backup worth adding

Any heater thermostat can stick. A controller like the Inkbird ITC-308 cuts power if the water gets too warm. If you’d rather read the set temperature on a display, the Fluval E Series is the digital alternative.