The JBJ Auto Top Off System


The JBJ Auto Top Off System is one of the most popular ATO systems on the market. Consisting of a simple controller with two float switches, it is one of the least expensive options currently available. It doesn’t have all the bells and whistles as some of the other auto top off systems but still offers limited redundancy via a maximum runtime timer and can be configured into three different modes.


The sensors on the JBJ auto top off system consist of two simple float switches. Each of the float switches attaches to the included mounting bracket, which in turn attaches to the lip of the sump. I don’t think that the brackets are as convenient as the magnet mounts you see with other systems but they are a significant improvement over the suction cups I have seen before. The ATO system is just too important and offers too much risk to be left to suction cups. If one came detached, your floors could get flooded, your tank could crash, etc.

The float switches themselves are the simple type, just a straight float switch on a bracket. No extra snail or splash guards, just a float switch mounted to a bracket. Very simple design so in that regard, it makes assembly pretty easy. The brackets themselves are easy to install and adjust the height.


The brain of the JBJ auto top off system is a simple white and black box with four indicator LED’s. The first LED is the “POWER” LED and lights to indicate that the unit has power. The second and third LED’s are the “SENSOR 1” and “SENSOR 2” LED’s. The LED’s turn on and off to indicate the reading from the float switches. The last LED indicator on the controller is the “PUMP” indicator. This LED activates when the pump turns on.

The controller has 3 different modes of operation (the differences are laid out down below in the “setup” section of this article. In terms of redundancy, the only form is that of a failsafe timer. Like other ATO systems with a failsafe timer, the timer activates when the pump turns on and if the pump runs for longer than the pre-programmed time the unit will go into failsafe mode, disabling the pump. In order to reset the system, you simply unplug the system from the wall and plug it back in.

The manual for the JBJ ATO system is pretty lacking so it’s worth mentioning a few features that aren’t mentioned anywhere in the standard manual. First is that the buzzer on the unit can be disabled. The instructions are available on their website and the reason it’s not likely mentioned in the normal manual is because the procedure is to open the unit up and rock the buzzer back and forth on the circuit board until it breaks off. Needless to say, this particular operation should be considered permanent.

The second detail is that the pump failsafe timing can be adjusted. This procedure also requires opening up the controller, but once inside it is as simple as using a screw driver to adjust a small potentiometer. Turning it all the way counter clockwise will bring the timer up to about 14 minutes. It’s worth noting that this shouldn’t be necessary. In the vast majority of circumstances if the timer is activating before the tank is finished topping off it is because a water change was done and the water level wasn’t filled back up to the sensor height, or the evaporation is faster than the top off pump. In either of those two circumstances, turning the timer up to 14 minutes wouldn’t fix the problem.

If you operate the controller in a latched mode (see “Mode B: Example 3 below) then you may need to increase the timer to ensure that there is enough time for your pump to fill from the low sensor to the high sensor. If increasing the timer isn’t sufficient then simply move the two float switches closer together (vertically). Of course, you could always do the later first or upgrade to a larger pump as well.


As mentioned before, the JBJ ATO system does not include its own pump. It supplies a standard 110V outlet that is capable of operating a pump that consumes up to two amps (about 200 watts). This should be an ample supply of power for just about any pump you might use for an auto top off. Most top off pumps will consume less than 20 watts.

For short runs and low demand the most popular pump to use is the Aqualifter pump from Tom’s Aquatics. This pump has a slow pump rate (3 gallons per hour) and only a 30” max head pressure so if you have a larger aquarium or need to pump further, a standard submersible pump like the Cobalt MJ1200 or one of the Sicce Syncra pumps will be a better choice.


There are three different modes that can be configured with the JBJ ATO system and the instructions are pretty scarce so I will do my best to lay out the differences. Each mode has its own ups and downs so pick the one that is best for your particular situation.

Mode A (Example 1):

Mode A is designed so that Sensor 1 is placed inside of the sump and Sensor 2 is placed at the bottom of your top off reservoir (just above your pump). Sensor 1 individually controls water level in the sump itself. Instead of using the second float switch in a latched mode, or as a backup sensor in the sump, it is used in the water reservoir as a run dry protection. In this setup, if you forget to fill up your top off reservoir the system will disable the ATO when the reservoir approaches empty to keep your pump from running dry. If you are using a submersible pump like a Cobalt MJ1200 or similar pump, this will help extend the life of your pump (running them dry is a good way to break them!). If you are using a pump that can run dry (like an Aqualifter), than this mode doesn’t have a lot of use for you. It could still be used to prevent the pump from running but it would only take a maximum of 14 minutes before the pump is turned off automatically.

Mode A (Example 2):

This particular example is essentially the same thing as example 1 except that you remove the second sensor and operate it as a single float switch system. There is no redundant backup float switch either in the sump or the ATO reservoir. For the most part, this particular mode isn’t one that is likely to be used very often.

Mode B (Example 3):

Mode B is the JBJ ATO’s latched mode. In latched mode you place two sensors in the sump. “Sensor 1” is placed as the high level and “Sensor 2” is the low sensor. When the water level drops to the point that low level sensor (Sensor 1) detects a low water level it will trigger the pump to turn on. The pump will engage and fill the tank until it is detected by the high water sensor (Sensor 2). This mode is useful if you want to make sure your system adds a minimum amount of water to the tank each time. If for example you have a tank with high evaporation, setup in Mode A the ATO may run very frequently. Using Mode B would allow you to move the sensors closer and farther apart (vertically) to adjust how much water is added each time and reducing the frequency with which the system runs.

In Mode B, it may be more likely that you have to adjust the internal timer to prevent it from turning the aquarium off before the water level reaches the max level sensor. If adjusting the timer to its max still doesn’t fill up far enough then you either need to use a larger pump or move the sensors closer together.


If you are looking for an auto top off system that is simple and doesn’t break the bank, the JBJ is a good choice. It offers the option to operate as a simple float system as well as offering a latched mode. If you’re looking for a simple and inexpensive float switch based top off system it is a great option. If you’re looking for a system that offers the highest level of redundancy though, you might want to look at a system like the Tunze Osmolator 3155.

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