Stability is one of the keys to success in our hobby. Fish need to be fed regularly. Tanks need to be cleaned frequently to prevent the buildup of wastes. Additives need to be dosed to maintain natural conditions. The more stable the system, the healthier it will be. This becomes especially important in managing delicate systems containing small polyp stony corals. Yet, too often, one of the most basic parameters—temperature—is overlooked.

The world's oceans are massive bodies of water covering the majority of the planet. Their enormous size makes them very resistant to rapid changes in environment. Still, scientists have observed entire sections of reef bleach and die after minor changes in temperature.

The small aquariums we keep do not benefit from the massive volume of the oceans. We must therefore be especially mindful of temperatures if we want to be successful. Employing a temperature controller can be a subtle, yet critical, tool for an aquarium. We will be covering three basic types of temperature controllers: single-stage, dual-stage and full-featured aquarium controllers. A single-stage controller is capable of controlling either heating or cooling, while a dual-stage controller can control both at the same time. A dual-stage controller ensures the cooling and heating systems are not running at the same time, saving electricity and preventing wear. A full-featured controller allows any number of devices to be controlled. For instance, low-wattage fans can be turned on to maintain temperature before the chiller kicks on, saving electricity. Heat producing lights can also be shut off if the temperature rises too high.

Programming a single-stage controller is pretty simple. Here we will be setting up an external controller to manage a fan on a nano tank. A good fan can drop the tank temperature a few degrees without the high cost of a chiller at the cost of increased evaporation. Because we do not want the fan running constantly (and evaporating water), we will use the controller to only turn on if it reaches a certain temperature.

First, let's get everything plugged in. There should be three cords coming out of the controller. The first cord should have a male plug that goes into a wall socket. The second cord should have a female receptacle that you will attach your controlled device to. The last cord has a temperature probe on the end that goes into the aquarium itself. Make sure the temperature probe is not resting against a pump or heater that may cause an incorrect reading.

To program the single-stage controller, press the Set button. The first option will be for Fahrenheit or Celsius. My American mind thinks in Fahrenheit, so I press up until it displays F.

Press Set again. S1 pops up in the upper left hand corner of the controller, signifying set point 1. We'll set it at 78°F, which is precisely where we want our fan to turn on.

Pushing Set again should bring up DIF1, for temperature differential. Set the temp differential to 1 or 2° so that the temperature does not fluctuate too much. Press the Set button once more to access heating or cooling mode. Our fan is a cooling device, so we will choose C1 for cooling device 1. Press Set one last time and programming is complete. The heater, which is controlled by its own thermostat in this system, should be set 1-2° below the setpoint on the fan.

Your controller is now up and running, kicking on a high powered fan when things get too toasty in the water. Inspect the heater and fan to make sure they are not running at the same time. Having a second thermometer for reference is also a very good idea.

A dual-stage controller is programmed similarly to the single-stage. Just set the heater to H2 or the second cooling device to C2 and also set DIF2 for 1-2°. A dual-stage controller will make sure the cooling device is not running at the same time as the heater, saving on electricity. Some chillers come with internal dual-stage controllers and include a socket to plug the heater into the chiller.

Let's move on to setting up a full-featured controller, the AquaController Jr., for our next demonstration.

Programming a full-featured controller is more complicated but provides a lot of additional features that make it well worth it. Of all the purchases I have made for my aquariums over the years, a controller has been the best by far. We're going to set up a heater, a fan, a chiller and our lights to keep everything nice and stable while keeping energy costs low.

An in-depth explanation of how to program every feature of the AquaController Jr. is beyond the scope of this article but we will cover the basic framework so you can understand how to make yours work right out of the box. Your controller may differ in design and programming but the basic principles are the same. Refer to your controller's manual for more detailed instructions or call us at 1-800-566-FISH for one-on-one support.

Our AquaController Jr. has eight power sockets that can all be independently controlled. For our demonstration, one socket will control a heater (HET), one will control the fan (FAN), one will control the chiller (CHI) and one will control the metal halide lighting (MH).

Each socket on the AquaController Jr. is given a name (listed above in ALL CAPS). Simple commands are then entered to tell each socket when to run.

Here is how the programs will look:


This will turn the heater on if the temperature falls below 78°. Most heaters also have their own internal thermostat. Set this to 79 or 80°, not to the max. Many aquarists have unfortunately made this mistake. Should your controller's temperature probe fail, you do not want your tank to turn into Cioppino.


his command will turn on our fans if the temperature rises to 78°. Setting this below the temperature the chiller turns on at will save electricity and chiller wear by cooling the system before the chiller kicks in.


The chiller will begin cooling once the temperature hits 78.5°. The fans will manage the temperature most of the time, saving your chiller for only the hottest part of the day. Some chillers even have internal temperature controllers. If that is the case, you can still use the AquaController Jr. to prevent your tank from crashing. If the temperature probe on the chiller fails, causing it to stick in the on position, you can set your AquaController Jr. to shut off the chiller only if it gets too cold with a command like:


Now onto the lighting:


Inserting this command has saved my tank from complete failure in the past, and is by itself worth the cost of a controller. One hot California day my chiller failed on me. Without this helpful little line my 400 Watt metal halide would have wiped out my entire aquarium. Instead, when the temperature hit a critical level, my lights shut off, saving everything.

So much of what we do depends on keeping our aquarium temperature stable. As the weather warms up, think about how the heat is affecting your aquarium and consider using a controller to keep things steady. From a simple controller to a full-featured aquarium management system, there are many options available to help you be successful.

Until next time... cool running my friends!