{"product_id":"eheim-thermocontrol-jager-125w-aquarium-heater","title":"EHEIM thermocontrol 125W Adjustable Aquarium Heater – 40 to 53 Gallons","description":"\u003cp\u003eThe EHEIM thermocontrol 125W Aquarium Heater, historically known as the EHEIM Jäger 125W, provides adjustable and precise temperature control for medium-sized freshwater and saltwater aquariums. EHEIM rates this model for aquariums from approximately 150 to 200 liters, equivalent to about 40 to 53 US gallons.\u003c\/p\u003e\n\u003cp\u003eThe temperature can be adjusted from approximately 65°F to 93°F, or 18°C to 34°C, allowing the heater to support a wide range of tropical freshwater fish, marine fish, planted aquariums, quarantine systems, and other temperature-sensitive setups.\u003c\/p\u003e\n\u003cp\u003eA special laboratory-glass jacket increases the heating surface and helps distribute heat evenly. The heater is completely submersible, includes automatic dry-run protection, and uses a visible control lamp to indicate when the heating element is operating.\u003c\/p\u003e\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e125-Watt Heating Output:\u003c\/strong\u003e Designed for aquariums from approximately 40 to 53 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdjustable Temperature:\u003c\/strong\u003e Select temperatures from approximately 65°F to 93°F\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRecalibratable Dial:\u003c\/strong\u003e Temperature scale can be corrected by approximately ±3.6°F when necessary\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrecise Temperature Control:\u003c\/strong\u003e Manufacturer-listed control accuracy of approximately ±0.9°F\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFully Submersible:\u003c\/strong\u003e Watertight construction allows complete underwater installation\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAutomatic Dry-Run Shutoff:\u003c\/strong\u003e Thermo Safety Control helps protect the heater if it is operated outside the water\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSpecial Laboratory Glass:\u003c\/strong\u003e Designed for efficient and even heat transfer\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHeating Indicator:\u003c\/strong\u003e Control lamp shows when the heater is actively heating\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDouble Suction-Cup Holder:\u003c\/strong\u003e Helps secure the heater to the aquarium wall\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFreshwater and Marine Compatible:\u003c\/strong\u003e Suitable for both freshwater and saltwater aquariums\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMade in Germany:\u003c\/strong\u003e Manufactured according to EHEIM’s aquarium-equipment standards\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eProduct Information\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e EHEIM\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCurrent Product Name:\u003c\/strong\u003e thermocontrol 125\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFormer\/Common Name:\u003c\/strong\u003e EHEIM Jäger 125W Heater\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eProduct Number:\u003c\/strong\u003e 3615010\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWattage:\u003c\/strong\u003e 125 watts\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRecommended Aquarium Volume:\u003c\/strong\u003e 150–200 liters\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eApproximate US Aquarium Volume:\u003c\/strong\u003e 40–53 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTemperature Range:\u003c\/strong\u003e 65–93°F \/ 18–34°C\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTemperature Control Accuracy:\u003c\/strong\u003e Approximately ±0.9°F \/ ±0.5°C\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCalibration Adjustment:\u003c\/strong\u003e Approximately ±3.6°F \/ ±2°C\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHeater Diameter:\u003c\/strong\u003e Approximately 36 mm \/ 1.4 inches\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHeater Length:\u003c\/strong\u003e Approximately 319 mm \/ 12.6 inches\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCable Length:\u003c\/strong\u003e Approximately 170 cm \/ 5.6 feet\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInstallation:\u003c\/strong\u003e Fully submersible\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAquarium Compatibility:\u003c\/strong\u003e Freshwater and saltwater\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Guarantee:\u003c\/strong\u003e Three years\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eBest Used For\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eAquariums between approximately 40 and 53 gallons\u003c\/li\u003e\n\u003cli\u003e40-gallon breeder aquariums\u003c\/li\u003e\n\u003cli\u003eFreshwater tropical community tanks\u003c\/li\u003e\n\u003cli\u003ePlanted aquariums\u003c\/li\u003e\n\u003cli\u003eAfrican and South American cichlid aquariums\u003c\/li\u003e\n\u003cli\u003eMarine fish aquariums\u003c\/li\u003e\n\u003cli\u003eQuarantine and hospital aquariums\u003c\/li\u003e\n\u003cli\u003eBreeding and conditioning systems\u003c\/li\u003e\n\u003cli\u003eAquariums requiring an adjustable temperature\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eAdjustable Temperature Range\u003c\/h3\u003e\n\u003cp\u003eThe EHEIM thermocontrol 125 can be adjusted from approximately 65°F to 93°F, or 18°C to 34°C.\u003c\/p\u003e\n\u003cp\u003eThis broad range allows the heater to be matched to the needs of different aquarium inhabitants. The correct temperature should always be selected according to the fish, shrimp, plants, corals, or other animals being maintained.\u003c\/p\u003e\n\u003cp\u003eDo not increase aquarium temperature solely because a heater can reach a higher setting. Excessively warm water holds less dissolved oxygen and may increase stress, metabolism, and disease progression.\u003c\/p\u003e\n\u003ch3\u003eTemperature Calibration\u003c\/h3\u003e\n\u003cp\u003eThe heater includes a recalibratable temperature scale. This allows the displayed setting to be corrected if the aquarium thermometer consistently shows a small difference from the selected temperature.\u003c\/p\u003e\n\u003cp\u003eEHEIM allows calibration adjustment of approximately ±2°C, equivalent to about ±3.6°F.\u003c\/p\u003e\n\u003cp\u003eBefore recalibrating:\u003c\/p\u003e\n\u003col\u003e\n\u003cli\u003eAllow the aquarium temperature to stabilize for at least 24 hours.\u003c\/li\u003e\n\u003cli\u003eUse a reliable independent aquarium thermometer.\u003c\/li\u003e\n\u003cli\u003ePlace the thermometer away from the heater.\u003c\/li\u003e\n\u003cli\u003eConfirm that water circulation is adequate.\u003c\/li\u003e\n\u003cli\u003eCompare the actual temperature with the heater setting.\u003c\/li\u003e\n\u003cli\u003eFollow the included EHEIM instructions to correct the dial.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003eDo not recalibrate the heater based on a single reading immediately after installation or a water change.\u003c\/p\u003e\n\u003ch3\u003eTemperature Control Accuracy\u003c\/h3\u003e\n\u003cp\u003eEHEIM lists a temperature-control accuracy of approximately ±0.5°C, equivalent to approximately ±0.9°F.\u003c\/p\u003e\n\u003cp\u003eThis does not mean that every area of the aquarium will remain at exactly the same temperature. Actual readings can be influenced by:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eWater circulation\u003c\/li\u003e\n\u003cli\u003eRoom temperature\u003c\/li\u003e\n\u003cli\u003eAquarium size and shape\u003c\/li\u003e\n\u003cli\u003eOpen-top or covered construction\u003c\/li\u003e\n\u003cli\u003eHeater placement\u003c\/li\u003e\n\u003cli\u003eFilter and pump operation\u003c\/li\u003e\n\u003cli\u003eAccuracy of the separate thermometer\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eCheck more than one area of the aquarium if a noticeable temperature difference develops between opposite ends of the tank.\u003c\/p\u003e\n\u003ch3\u003eRecommended Aquarium Size\u003c\/h3\u003e\n\u003cp\u003eEHEIM rates the thermocontrol 125 for aquariums of approximately 150 liters and up to about 200 liters. This equals approximately 40–53 US gallons.\u003c\/p\u003e\n\u003cp\u003eThe correct heater wattage depends on more than gallon capacity. Consider:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eThe difference between room temperature and desired water temperature\u003c\/li\u003e\n\u003cli\u003eWhether the aquarium has a lid\u003c\/li\u003e\n\u003cli\u003eCold drafts and exterior walls\u003c\/li\u003e\n\u003cli\u003eOpen-top evaporation\u003c\/li\u003e\n\u003cli\u003eWater circulation\u003c\/li\u003e\n\u003cli\u003eAdditional water in a sump\u003c\/li\u003e\n\u003cli\u003eThe aquarium’s exposed surface area\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eA 125W heater may be appropriate for a covered 50-gallon aquarium in a warm room but may not provide enough heat for the same aquarium in a cold basement.\u003c\/p\u003e\n\u003ch3\u003eEHEIM thermocontrol Heater Sizing Guide\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e25W:\u003c\/strong\u003e Approximately 5–7 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e50W:\u003c\/strong\u003e Approximately 7–16 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e75W:\u003c\/strong\u003e Approximately 16–26 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e100W:\u003c\/strong\u003e Approximately 26–40 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e125W:\u003c\/strong\u003e Approximately 40–53 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e150W:\u003c\/strong\u003e Approximately 53–79 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e200W:\u003c\/strong\u003e Approximately 79–106 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e250W:\u003c\/strong\u003e Approximately 106–159 gallons\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e300W:\u003c\/strong\u003e Approximately 159–264 gallons\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThese conversions are based on EHEIM’s published liter ranges. Room conditions may require choosing a different wattage or using more than one heater.\u003c\/p\u003e\n\u003ch3\u003eSpecial Laboratory-Glass Construction\u003c\/h3\u003e\n\u003cp\u003eThe heater jacket is made from special laboratory glass designed to resist chemical and biological substances in aquarium water.\u003c\/p\u003e\n\u003cp\u003eAccording to EHEIM, the glass jacket:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIncreases the effective heating surface\u003c\/li\u003e\n\u003cli\u003eHelps distribute heat evenly\u003c\/li\u003e\n\u003cli\u003eActs as a heat shield around the internal heating element\u003c\/li\u003e\n\u003cli\u003eResists normal temperature fluctuations associated with aquarium use\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe glass should not be described as completely shatterproof. Inspect the heater before every installation and discontinue use if the glass is cracked, chipped, or damaged.\u003c\/p\u003e\n\u003ch3\u003eThermo Safety Control\u003c\/h3\u003e\n\u003cp\u003eThe EHEIM thermocontrol includes automatic dry-run shutoff, known as Thermo Safety Control.\u003c\/p\u003e\n\u003cp\u003eThis feature is intended to switch the heater off if it is accidentally operated outside the water. It helps reduce the risk of overheating and damage but should not replace proper aquarium-heater handling.\u003c\/p\u003e\n\u003cp\u003eAlways unplug the heater before:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eLowering the water level\u003c\/li\u003e\n\u003cli\u003ePerforming a water change\u003c\/li\u003e\n\u003cli\u003eRemoving the heater\u003c\/li\u003e\n\u003cli\u003eCleaning the aquarium\u003c\/li\u003e\n\u003cli\u003ePlacing hands in the water\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eHeating Indicator Light\u003c\/h3\u003e\n\u003cp\u003eThe control lamp indicates when the heater is actively producing heat. It normally switches on when the aquarium temperature falls below the selected setting and turns off once the thermostat reaches the target.\u003c\/p\u003e\n\u003cp\u003eNormal cycling is expected. The light does not need to remain illuminated continuously for the heater to maintain temperature.\u003c\/p\u003e\n\u003cp\u003eIf the indicator remains on continuously while the water stays below the selected temperature, the heater may be undersized, improperly positioned, or affected by unusually cold room conditions.\u003c\/p\u003e\n\u003ch3\u003eInstallation Instructions\u003c\/h3\u003e\n\u003col\u003e\n\u003cli\u003eInspect the heater, glass tube, cord, plug, holder, and suction cups.\u003c\/li\u003e\n\u003cli\u003eDo not use the heater if any part appears damaged.\u003c\/li\u003e\n\u003cli\u003eAttach the double suction-cup holder.\u003c\/li\u003e\n\u003cli\u003ePosition the heater fully underwater.\u003c\/li\u003e\n\u003cli\u003eInstall it where steady water circulation can distribute heat.\u003c\/li\u003e\n\u003cli\u003eAllow the heater to acclimate to the aquarium water before plugging it in.\u003c\/li\u003e\n\u003cli\u003eCreate a drip loop in the electrical cord below the outlet.\u003c\/li\u003e\n\u003cli\u003eSelect the desired temperature.\u003c\/li\u003e\n\u003cli\u003eConnect the heater to power.\u003c\/li\u003e\n\u003cli\u003eVerify the actual temperature with a separate thermometer.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003eRead and follow the complete EHEIM operating manual supplied with the heater.\u003c\/p\u003e\n\u003ch3\u003eHorizontal or Vertical Installation\u003c\/h3\u003e\n\u003cp\u003eThe thermocontrol heater may be installed according to the aquarium layout as long as it remains fully submerged and water can circulate freely around the glass jacket.\u003c\/p\u003e\n\u003cp\u003eHorizontal or angled placement low in the aquarium can help distribute heat as warmer water rises. Vertical placement may be more convenient beside a filter intake or return.\u003c\/p\u003e\n\u003cp\u003eDo not bury the heater in substrate or allow it to rest directly against rocks, wood, decorations, or the aquarium bottom.\u003c\/p\u003e\n\u003ch3\u003eBest Heater Placement\u003c\/h3\u003e\n\u003cp\u003ePlace the heater near a canister-filter return, hang-on-back filter output, internal filter, or circulation pump. Moving water carries heat throughout the aquarium and helps prevent warm and cool zones.\u003c\/p\u003e\n\u003cp\u003eAvoid placing the heater:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIn a stagnant corner\u003c\/li\u003e\n\u003cli\u003eBehind solid decorations that block flow\u003c\/li\u003e\n\u003cli\u003eDirectly beneath loose rocks\u003c\/li\u003e\n\u003cli\u003eWhere fish can wedge it against the aquarium wall\u003c\/li\u003e\n\u003cli\u003eWhere the water level may fall below it during maintenance\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eUsing a Separate Thermometer\u003c\/h3\u003e\n\u003cp\u003eAlways use a separate aquarium thermometer with the EHEIM thermocontrol heater.\u003c\/p\u003e\n\u003cp\u003eThe thermometer should be positioned away from the heater so it measures the general aquarium temperature rather than the warmer water surrounding the heating element.\u003c\/p\u003e\n\u003cp\u003eA separate thermometer helps identify:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIncorrect dial settings\u003c\/li\u003e\n\u003cli\u003eCalibration differences\u003c\/li\u003e\n\u003cli\u003eInsufficient heater wattage\u003c\/li\u003e\n\u003cli\u003ePoor water circulation\u003c\/li\u003e\n\u003cli\u003eEquipment failure\u003c\/li\u003e\n\u003cli\u003eUnexpected seasonal temperature changes\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eWater-Change Safety\u003c\/h3\u003e\n\u003cp\u003eUnplug the heater before lowering the aquarium water level. Allow the heater to cool while it remains submerged before removing it or exposing the glass to air.\u003c\/p\u003e\n\u003cp\u003eAfter refilling the aquarium, confirm that the heater is fully submerged and allow the glass to acclimate to the new water temperature before reconnecting power.\u003c\/p\u003e\n\u003cp\u003eAvoid pouring significantly colder replacement water directly onto a hot heater.\u003c\/p\u003e\n\u003ch3\u003eFreshwater Aquarium Use\u003c\/h3\u003e\n\u003cp\u003eThe EHEIM thermocontrol 125 is suitable for freshwater tropical community tanks, planted aquariums, cichlid systems, quarantine tanks, and breeding setups within its recommended volume range.\u003c\/p\u003e\n\u003cp\u003eThe adjustable thermostat allows customers to select a temperature appropriate for the particular freshwater species rather than relying on a fixed preset value.\u003c\/p\u003e\n\u003ch3\u003eSaltwater Aquarium Use\u003c\/h3\u003e\n\u003cp\u003eEHEIM approves the thermocontrol heater for marine and saltwater aquarium use.\u003c\/p\u003e\n\u003cp\u003eInspect the heater, holder, suction cups, and cord regularly for salt creep and mineral accumulation. Disconnect the heater from power before cleaning.\u003c\/p\u003e\n\u003cp\u003eFor valuable marine systems, consider pairing the heater with an independent temperature controller or alarm for additional monitoring.\u003c\/p\u003e\n\u003ch3\u003eUse in Planted Aquariums\u003c\/h3\u003e\n\u003cp\u003eThe heater may be used in planted aquariums when its wattage and selected temperature are suitable for the plants and livestock.\u003c\/p\u003e\n\u003cp\u003ePosition the heater where dense plant growth will not restrict circulation or conceal the heater during inspection.\u003c\/p\u003e\n\u003cp\u003eThe heater controls temperature only. It does not supply light, carbon dioxide, fertilizer, or minerals.\u003c\/p\u003e\n\u003ch3\u003eUse with Shrimp\u003c\/h3\u003e\n\u003cp\u003eThe adjustable temperature range allows the thermocontrol 125 to be used in appropriately sized shrimp aquariums, provided the selected temperature matches the species.\u003c\/p\u003e\n\u003cp\u003eSome Neocaridina shrimp tolerate warmer tropical temperatures, while many Caridina species perform better at cooler temperatures. Warmer water also contains less dissolved oxygen.\u003c\/p\u003e\n\u003cp\u003eResearch the specific shrimp species and monitor the aquarium with an independent thermometer.\u003c\/p\u003e\n\u003ch3\u003eUse in Quarantine and Hospital Tanks\u003c\/h3\u003e\n\u003cp\u003eThe adjustable temperature dial can be useful in quarantine and observation systems where the temperature must be matched to a particular fish species.\u003c\/p\u003e\n\u003cp\u003eDo not increase temperature automatically during illness. Some infections progress faster at elevated temperatures, and certain medications or fish species require specific temperature limits.\u003c\/p\u003e\n\u003cp\u003eFollow an appropriate diagnosis and treatment plan rather than using heat as a universal disease treatment.\u003c\/p\u003e\n\u003ch3\u003eOne Heater vs. Two Smaller Heaters\u003c\/h3\u003e\n\u003cp\u003eSome medium and large aquariums may benefit from using two smaller heaters placed at opposite ends of the tank. This arrangement can improve heat distribution and provide limited backup if one unit stops operating.\u003c\/p\u003e\n\u003cp\u003eThe combined wattage should still match the aquarium’s total volume and room conditions. Two heaters do not eliminate the need for a thermometer or routine inspection.\u003c\/p\u003e\n\u003ch3\u003eCleaning and Maintenance\u003c\/h3\u003e\n\u003col\u003e\n\u003cli\u003eDisconnect the heater from power.\u003c\/li\u003e\n\u003cli\u003eAllow it to cool while submerged.\u003c\/li\u003e\n\u003cli\u003eRemove it carefully from the aquarium.\u003c\/li\u003e\n\u003cli\u003eWipe away algae and mineral buildup with a soft cloth or sponge.\u003c\/li\u003e\n\u003cli\u003eInspect the laboratory-glass jacket for cracks or damage.\u003c\/li\u003e\n\u003cli\u003eInspect the power cord, plug, holder, and suction cups.\u003c\/li\u003e\n\u003cli\u003eRinse according to the manufacturer’s directions.\u003c\/li\u003e\n\u003cli\u003eReinstall the heater fully underwater.\u003c\/li\u003e\n\u003cli\u003eAllow it to acclimate before reconnecting power.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003eDo not use abrasive pads, sharp scrapers, soap, bleach, or household cleaning chemicals.\u003c\/p\u003e\n\u003ch3\u003eElectrical Safety\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eCreate a drip loop below the electrical outlet\u003c\/li\u003e\n\u003cli\u003eUse a GFCI-protected outlet whenever possible\u003c\/li\u003e\n\u003cli\u003eKeep the plug and electrical connection dry\u003c\/li\u003e\n\u003cli\u003eDo not handle the plug with wet hands\u003c\/li\u003e\n\u003cli\u003eUnplug aquarium equipment before placing hands in the water\u003c\/li\u003e\n\u003cli\u003eNever use a heater with cracked glass or a damaged cord\u003c\/li\u003e\n\u003cli\u003eDo not pull or carry the heater by the power cord\u003c\/li\u003e\n\u003cli\u003eDo not cut, splice, or repair the electrical cord\u003c\/li\u003e\n\u003cli\u003eOperate the heater only while properly submerged\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eImportant Aquarium Heater Note\u003c\/h3\u003e\n\u003cp\u003eNo aquarium heater should be considered completely fail-proof. Use an independent thermometer and check aquarium temperature regularly.\u003c\/p\u003e\n\u003cp\u003eThe EHEIM thermocontrol 125 is rated for approximately 40–53 gallons, but actual heating ability depends on room temperature, aquarium design, lid coverage, circulation, and the required temperature increase.\u003c\/p\u003e\n\u003cp\u003eAutomatic dry-run protection is an additional safety feature, not permission to operate the heater outside the water.\u003c\/p\u003e\n\u003cp\u003eAlways unplug the heater before water changes, cleaning, removal, or aquarium maintenance.\u003c\/p\u003e\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eIs this the same heater as the EHEIM Jäger 125W?\u003c\/strong\u003e\u003cbr\u003eThe current official name is EHEIM thermocontrol 125. It is the modern continuation of the heater commonly known as the EHEIM Jäger.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat size aquarium is the 125W heater designed for?\u003c\/strong\u003e\u003cbr\u003eEHEIM rates it for approximately 150–200 liters, equivalent to about 40–53 US gallons.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it only for aquariums up to 40 gallons?\u003c\/strong\u003e\u003cbr\u003eNo. EHEIM’s official range extends from approximately 40 to 53 gallons under suitable conditions.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is the adjustable temperature range?\u003c\/strong\u003e\u003cbr\u003eThe temperature can be set from approximately 65°F to 93°F, or 18°C to 34°C.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan the temperature dial be calibrated?\u003c\/strong\u003e\u003cbr\u003eYes. The displayed setting can be recalibrated by approximately ±3.6°F, or ±2°C.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow accurate is the thermostat?\u003c\/strong\u003e\u003cbr\u003eEHEIM lists a temperature-control accuracy of approximately ±0.9°F, or ±0.5°C.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs the glass shatterproof?\u003c\/strong\u003e\u003cbr\u003eEHEIM uses durable special laboratory glass, but no glass aquarium heater should be described as completely shatterproof.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs the heater fully submersible?\u003c\/strong\u003e\u003cbr\u003eYes. EHEIM describes it as watertight and completely submersible.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it have dry-run protection?\u003c\/strong\u003e\u003cbr\u003eYes. Thermo Safety Control automatically switches the heater off if it is accidentally operated outside the water.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it have an indicator light?\u003c\/strong\u003e\u003cbr\u003eYes. A control lamp indicates when the heater is actively heating.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan it be installed horizontally?\u003c\/strong\u003e\u003cbr\u003eIt may be positioned according to the included instructions as long as it remains fully submerged and has adequate water circulation.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan it be used in freshwater?\u003c\/strong\u003e\u003cbr\u003eYes. It is suitable for freshwater aquariums.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan it be used in saltwater?\u003c\/strong\u003e\u003cbr\u003eYes. EHEIM approves the thermocontrol heater for marine aquarium use.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it suitable for planted aquariums?\u003c\/strong\u003e\u003cbr\u003eYes, provided the selected temperature is suitable for the plants and livestock.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eShould I use a separate thermometer?\u003c\/strong\u003e\u003cbr\u003eYes. An independent thermometer is recommended to verify the actual aquarium temperature.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eShould the heater be unplugged during water changes?\u003c\/strong\u003e\u003cbr\u003eYes. Disconnect it before lowering the water level and allow it to cool before exposing or removing it.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow long is the heater?\u003c\/strong\u003e\u003cbr\u003eThe 125W model is approximately 319 mm, or 12.6 inches, long.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow long is the power cable?\u003c\/strong\u003e\u003cbr\u003eThe cable is approximately 170 cm, or 5.6 feet.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes the heater include mounting hardware?\u003c\/strong\u003e\u003cbr\u003eYes. It includes a double suction-cup holder.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is the manufacturer guarantee?\u003c\/strong\u003e\u003cbr\u003eEHEIM lists a three-year manufacturer guarantee for the thermocontrol 125.\u003c\/p\u003e\n\u003ch3\u003eAvailable at Tropical Treasures Wyo\u003c\/h3\u003e\n\u003cp\u003eThe EHEIM thermocontrol 125W Adjustable Aquarium Heater provides precise, recalibratable temperature control for freshwater and saltwater aquariums between approximately 40 and 53 gallons. Its special laboratory-glass jacket, adjustable 65–93°F range, heating indicator, automatic dry-run shutoff, and double suction-cup holder make it a dependable choice for medium aquarium systems.\u003c\/p\u003e\n\u003cp\u003eVisit Tropical Treasures Wyo in Cheyenne, Wyoming, to shop EHEIM aquarium heaters, filters, replacement parts, thermometers, temperature controllers, and aquarium equipment.\u003c\/p\u003e","brand":"Tropical Treasures Wyo LLC","offers":[{"title":"Default Title","offer_id":52129721450709,"sku":null,"price":30.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0670\/4545\/8133\/files\/720686361379.jpg?v=1759326089","url":"https:\/\/tropicaltreasureswyo.com\/products\/eheim-thermocontrol-jager-125w-aquarium-heater","provider":"Tropical Treasures Wyo LLC","version":"1.0","type":"link"}