Your cart
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.  We do not recommend the use of the backup float when connected to our peristaltic pump.  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

Based on 41 reviews
5 Star
4 Star
3 Star
2 Star
1 Star
Write a Review Ask a Question
  • Reviews (41)
  • Questions (3)

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!
Grant Hultman


I have had this ATO for about 2 years! The ATO has never failed me! I plan to use them on any tank I ever own. Only issue is that the float valve that came with my setup has a completely rusted wing nut. This is obviously not ideal and frustratin.

Alexey T.
United States

Excellent product and support

I have this kit for almost year and it working great. At some point had to move it to another tank, didn't connect tubing secure and pump stopped pulling water, wrote e-mail and in less than hour had response from the support, which correctly diagnosing my issue and described how to fix it.

Fernando R.
United States


To be used in tank build to compare with other types

Mark T.
United States

Better than Neptune ATK

Pressure sensor so much more reliable than optical sensors.

Ana E.
United States

My experience with the ATO by AVAST

When I first tried to set it up I was having great difficulties figuring out the instructions on the AVAST website. I could not get the ATO to kick on when it needed too or off when it was full. I overflowed my sump once and made a mess! Finally I decided to contact AVAST customer service. I should have done that right away! Justin helped first and then Dan. There were in daily contact with me via email and even offered their number if it were easier to communicate. AMAZING customer service. Once I was able to get the settings correct and the air bubble out of the tubing, the ATO began and is currently running flawlessly! Thank you Justin and Dan for all your help! I will definitely purchase from AVAST again!