Why You’ll Love It
Using an upgraded titanium steel rod, the hygger 921 aquarium heater has the fastest 5-second warming and very strong corrosion resistance. It fully utilizes thermal energy inertia to reach the set temperature and saves energy for freshwater fish tanks of 60–180 gallons.
Key Features
Fast Heating
The heating element is made of stainless steel, enabling rapid water heating and facilitating quick temperature adjustments as needed. It is explosion-proof and anti-corrosion, with no electrical leakage. The included strong suction cups can stably fix the heater in every corner of the fish tank.

External IC Temperature Controller
The controller has 4 kinds of work instructions – Working/Malfunction/ Thermostatic/ Out of water. It displays real-time water temperature or set temperature, a three-digit display, a water temperature displays accurate to ± 1°F, and is easy to read.
Anti-dry Protection
When the heating rod is exposed to air, it displays an ER fault code, and the heater will shut off automatically. When the heating rod is completely immersed in water, it will start working automatically. The heater allows for precise temperature adjustments ranging from 70 to 94°F, suitable for larger freshwater fish tanks, 60–180 gallons.

Overheating Protection
Over-temperature protection system, when the temperature in the tank is over 97 °F, it will stop heating, to avoid fish from boiling due to high temperature. When the water temp exceeds about 93.5 °F, start alternately flashing the EE fault code; over 97℉, the heater will stop heating automatically.

Power-off Memory Function
When the water temp cools down to 93℉, the heater will start working automatically. In addition, it has a power-off memory function, and no need to set it again after a power outage.
Dual Relay System & ABS Protective Sleeve
This HG921 heater offers enhanced safety, equipped with a dual relay design, a double temperature probe prevents the single temperature probe from being damaged and causing no heating or over temperature. The ABS protective sleeve prevents harm to small fish.

Usage Tips
- When using this heating, the heating should be submersible in the water and should not be exposed to the water surface.
- It is necessary to regularly clean and clean the heating plate. If the heating plate is attached with impurities, the heating efficiency will be reduced.
- Connect the heater to power, and the IC temperature controller will display the current water temperature.
- Press the “Set” button to adjust the temperature to your desired level. The display will flash the set temperature value three times before showing the current water temperature.
4 Digital Display Models
1. Working: The heater is actively heating the water, indicated when the display shows this mode.
2. Malfunction: If there’s an issue, the display will show a fault code to alert you of the problem.
3. Thermostatic: This mode is indicated when the water temperature reaches the desired value.
4. Out of Water: If the heating rod is not submerged, the display will show the error code “Er,” and the heater will cease operation until the issue is resolved.
Error Code Explanations and Solutions

Er: The heating rod is exposed to the air. To resume heating, ensure that it is fully submerged in water.
EH: The water temperature exceeds 97°F. Allow the water to cool to a safe temperature before the heater can operate again.
EC: There was a communication failure between the heater components. If this error occurs, the heater should be replaced, as it cannot be fixed.
E3: The relay has melted, causing the heater to fail. It must be discarded and replaced.
H1: The temperature sensor is in a short-circuit protection mode. This indicates a severe issue with the heater, and it should be discarded.
Specification















This heater has been amazing,best one i ever owned.I had mine for about 4 years.I have a 200 gallon African cichlid tank,from the day I bought it,I set it to 79 degrees and walked away,up until today received an E3 code,tried to find a fix,nope relay melted.But I will own another that’s for sure.But besides the relay,well built guys.
Love it makes life easy in the tank great value