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Auto Top Off

Auto Top Off

$ 99.99

Finally, a top-off control sensor that is mounted to your sump with a magnet rather than a clunky bracket!  Driven by a pressure-sensitive switch located in the relay box, a strong magnetic field won't affect its operation.  The sensor tube can't get clogged with calcium deposits or activated by wayward snails as there are no moving parts.  Our top-off system is capable of maintaining the sump water level within +/- 1/4" tolerance (1/2" overall) and features a built-in range buffer or hysteresis effect, which prevents rapid on-off switching that sometimes occurs when cheap float switches bob up and down in small waves.  The magnet bracket is capable of holding on up to 1/2" thick glass.  The slim design relay box is unobtrusive and can handle up to a 3 amp pump at 110v AC.  The green LED light indicates when the circuit is active and the pump is running.

The magnetic bracket also contains both an adjustable 1/4" to 1/2" fitting, useful for holding the tube from your top-off pump in place.  This fitting can be switched out for an optional backup mechanical float valve, which will physically close and stop the flow from your pump in the event of an electrical or switch issue.  Read more about choosing the correct pump for ATO usage here.

Our digital output version is now available for use with most aquarium controllers.  This version is designed without an outlet; just plug the ATO pump into your controller's relay box and set up the controller to read the pressure switch state (see instruction manual for details).  It is available with the plug types of several popular aquarium controllers.  For example, Neptune Apex uses a "minidin-8" style plug.  To use this, simply plug into the port marked "I/O" on the controller, and program according to instructions.  If you already have something plugged in to that port, you will want to use their Breakout Box and select the "bare wire" option below.  See instruction manual for further details. Bare wire connection is 2 strand, non-polarized 22 AWG shielded wire. In the case of ReefKeeper Lite/Elite, use this option with the float switch adapter wire that came with your controller and/or SW5 Switch Module.

Cerebra, Reef Angel, and RKL/RKE compatible plugs are also available.
The Digital Output version allows several non-standard uses for this switch. For example, it can be a low level sensor in your sump that is impervious to coralline algae and snails, can turn off your return pump and send you a text message at the same time. There are a lot of options since you can reverse the logic of the switch at the controller.

Our switch and all components are made in the USA. 

Technical Data:

Water level sensitivity: 1/2" 
Magnet strength: up to 1/2" glass
Magnet bracket dimensions: 1-3/4" front to back x 2-1/4" wide (excluding external magnet half, 1/2" thick)
Switch box dimensions: 4" x 2.25" 
Input power: AC 110v
Relay box capacity: 3 amps
Switch rating: 10+ million cycles
Warranty: 1 year

Click here for Standard outlet box ATO installation manual
Click here for Digital output ATO installation manual

Customer Reviews

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David E.
United States

Best ATO

Best ATO I have ever used. I have it monitored by my apex . Water level is rock solid. Set it and forget it. Place the switch box next to your ear as the tube enters the water to set your water level and never worry again.

Daniel H.
United States

Auto Top off

Responses to my questions were very quick and helpful. Excellent service and the auto top off works great. Thanks!!

Ryan S.


I'm now using these switches on several devices and have been for a year now. The only thing I've changed is I clamp a short chunk of silicon tube between the airline and box. I never want to be too cautious for air leaks, only downside is it's not easily removable after you do that. Still way better then various other methods and significantly lower chances of error then optical or a physical float switch.

Antonio C.
United States

Phenomenal ATO

The simplicity of this ATO and knowing I never have to worry about cleaning it to work properly is the best investment I could ask for. Thank you Avast Marine!

Eric S.
United States

Auto Top Off with Peristaltic Pump

Works flawlessly with my Apex controller. I have used a Spectrapure Litermeter for years, which recently died, and had to constantly monitor my sump level and adjust the pump accordingly. This auto top off keeps the sump level at a completely steady level all the time. The peristaltic pump works perfectly for me since my reservoir is on the opposite side of the room from my sump so it pumps up, across the ceiling, and down into my sump. Great product!