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Setting your Aquarium Heater

How do I Adjust the Setting of the Heater in My Fish Tank?

(The First Tank Guide)

Though aquarium heaters are very common, there are often questions about setting them. You should be able to use the same technique for setting a chiller if you are using one, as the adjustment being made is to the thermostat, not the heater element.

Preset Aquarium Heaters

There are many models of aquarium heaters on the market today that come 'preset' or with a temperature gauge on the side of the heater or on the control knob to help you set the temperature. Though these can be very helpful in getting the thermostat in the right range, they should be viewed with some skepticism when you are adjusting your thermostat. Though some manufacturers make claims otherwise, these gauges are at best accurate within two or three degrees Fahrenheit (one to one and a half degrees Celsius), and will get less accurate over the life of the heater. With this in mind, it is still important to monitor and adjust the thermostat setting on the heater as necessary, rather than just assuming the markings on the heater are correct.

Some other preset aquarium heaters claim that are set to the correct temperature t the factory and need no adjustment. These should be viewed with even greater scepticism, and probably should be avoided. Since these heaters have no way to adjust the temperature, you cannot set the temperature correctly for your fish that prefer warmer or cooler water, and you have no option to elevate the temperature in the tank in case of disease. An aquarium heater without an adjustable thermostat also means that the heater cannot be adjusted to account for differences in power stability or for age of the heater and components.

Non-Preset Aquarium Heaters

Non-preset aquarium heaters are less expensive than their preset counterparts - often as little as half the price. If you choose a non-preset aquarium heater, you should avoid adjusting the thermostat setting until you have the heater set up in the tank and are ready to monitor and properly adjust the thermostat. Even though these heaters are not "pre-set," they are usually set to about the correct temperature anyway.

Setting Your Aquarium Heater or Chiller

Setting your aquarium heater should be relatively easy, but it may be time consuming, depending on how easy it is to adjust the thermostat control, how close to the correct temperature your heater is to begin with, and how good you are at making very fine adjustments with the thermostat control.

When adjusting your thermostat, it is important to make very small adjustments. The thermostats for these devices are usually very sensitive and set to only operate in a limited range, so large or gross adjustments can make a very big difference in temperature.

To set your aquarium heater, you will first want to have the heater set up in the aquarium as you will want it long term. Check with the manufacturer's recommendation s for installing and positioning your heater. Once the heater is installed, let is sit for at least half an hour to be sure the temperature has equalized before plugging the heater in. Before plugging the heater in, also check the aquarium temperature to determine whether the water needs to be warmed from its current temperature or not. For this you will need a separate thermometer.

Once the heater is in place and plugged in, check to see if the indicator light is on. Your heater should have an indicator light (usually red or orange) to indicate whether the heater is currently heating. If the heater is on, turn the thermostat control down carefully until the indicator light just turns off. Do this whether the water temperature is too cool or not. Leave the heater for at least half an hour and then come back and check the temperature.

If the tank still needs to be warmed up, wait until the indicator light on the heater is off and then carefully turn the thermostat up until the light just turns on. Once the light comes on, leave the heater for another half hour or more. If the temperature is still too cool after the half hour, repeat this procedure. If the temperature is correct, you are done. If the temperature is too warm, follow the next step to lower the temperature.

If the tank is too warm, wait until the indicator light on the heater is on and then carefully turn the thermostat down until the light just turns off. Once the light turns off, leave the heater for another half hour or more. If the temperature is still too warm, repeat this step until the temperature is correct. If the temperature is correct, you are done. If the temperature is too cool, follow the previous instructions to raise the setting of the thermostat.

Digital Thermostats

If you have a separate digital thermostat, you will probably need to calibrate this thermostat following directions provided by the manufacturer. However, once the digital thermostat is calibrated, you should be able to set your temperatures and then plug your heater and/or chiller into the thermostat without going through the process of adjusting that is necessary with traditional analog thermostats. However, it is still important to monitor the temperature in your aquarium with a thermometer.

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