Heater
Maintains the water temperature constant at the desired value. Indispensable for tropical aquariums in environments where the ambient temperature drops below 24 degrees.
Detailed explanation
Temperature is a critical parameter because fish are cold-blooded animals. They cannot regulate their own body temperature and are completely dependent on the water around them.
Immersion heaters with an integrated thermostat are the most popular. They are positioned in the aquarium or in the sump and adjusted to the desired temperature. The recommended power is approximately 1 watt per litre but depends on the difference between ambient temperature and target temperature.
Titanium heaters are more resistant and do not break like glass ones. They cost more but eliminate the risk of a broken heater killing fish through overheating or contact with water.
External temperature controllers (like the Inkbird or Aqua Medic T-controller) add a layer of safety. They monitor the temperature with a separate probe and turn off the heater if it exceeds the set limit.
In marine aquariums the ideal temperature is between 24 and 26 degrees. Corals are very sensitive: bleaching begins above 28 degrees. In summer you may need a cooler rather than a heater.
In tropical freshwater aquariums the range depends on the species. Discus want 28-30 degrees. Most tropical fish do well at 24-26.
Cold water fish (goldfish, koi) do not need a heater. Indeed, temperatures that are too high shorten their life.
The heater is not used in ponds. Pond fish are bred to tolerate outdoor temperatures, including winter frost.
Reference values by aquarium type
| Aquarium type | Recommended range |
|---|---|
| Marine (reef) | 24 - 26 °CAbove 28°C bleaching risk for corals |
| Tropical freshwater | 24 - 28 °CDiscus: 28-30°C |
| Coldwater / pond | 4 - 22 °CGoldfish and koi tolerate 4 to 30°C but prefer 15-22°C |
| Brackish | 24 - 28 °C |
How it is measured
Digital thermometer with probe or liquid crystal thermometer glued to the glass. The digital probe is more precise. Place the thermometer away from the heater to read the actual temperature of the aquarium.
What happens when it is too low
Tropical fish become lethargic, stop eating, immune system weakens. Filter bacteria slow down. Under 18°C most tropicals die.
What happens when it is too high
Dissolved oxygen decreases. The fish breathe heavily on the surface. Corals expel zooxanthellae (bleaching). Accelerated metabolism increases ammonia production.
Coralia Lab monitors this parameter with AI diagnostics. Tank Score alerts you when a value moves outside the recommended range for your aquarium.
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