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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

4.9 Based on 68 Reviews
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  • auto top
Glenn S.
Canada Canada

Avast ATO

ATO is compact and simple. No gimmicks or sensors you need to worry about. Very happy with my purchase.

Art N.
United States United States

Avast ATO > All

Setup was a breeze even though there were no instructions in the box, the apex digital out is awesome.

Michael E.
United States United States


IMO this is the best ATO out there. Great product.

Christopher O.
United States

Best ATO for any system.

This ATO is pressure sensitive, so as long as it is installed correctly it will fil any size system or return pump area. I have used this ATO on a nano, a large 250 gallon bin, and a traditional sump with a return section. Works in any spot and allows you to keep water levels consistent.

Brad M.
United States

Avast ato

Ato is great!!! No need for a water storage tank with the back up float valve. I ran a line from dt on first floor, into the basement and 30’ over to my ro storage, diaphragm pump handles it no prob. Yeah its noisy but its not on much and it serves its purpose. The pressure sensor is an awesome addition, i get about a 1/2” fluctuation in sump, which doesnt affect salinity in my 150 gallon setup. Overall i wanna ditch my tunze ato in my other tank for another avast. Again great product and so far been solid. Nice to not have to carry rodi up stairs.