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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.  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

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  • Reviews (48)
  • Questions (4)

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Ryan Snodgrass

1yr strong.

I'm a huge fan of the pressure switch. Everyone talks about optical, float, etc but they all have multiple points of failure beyond an actual switch failure. These only have 1... if the switch fails. I'm likely going to buy a second unit as a backup but haven't yet and two more to rig up an automatic filling station for my ro.

karen sorensen
waterford ny

a must have

simple to set up plenty of wire and pressure switch line to set up on any size tank. magnetic mount is strong and can used to add probes or ro line. shipping is lightning fast. plus made in the USA thanks for making great products

joey w.
United States

Two thumbs up.

Very simple and straightforward design that works. I have this installed on an IM 25g lagoon.

Jeff T.
United States


After extensive research I decided on this Avast ATO system. And I researched them ALL. Seems like there where negative reviews on every other product out there. There usually is on any product though. Being pressure switch controlled and no moving parts was a plus. Seems to be a solid product build wise. And made in the USA! Time will tell on the reliability but according to others it’s a solid performer. When I installed the switch control box in my cabinet next to the tank, the supplied tubing wasn’t quite long enough to reach from the sump where the acrylic tube and magnet holder where located back to the cabinet. That being said, you can remove the rigid line from the tube and install another line thats longer. I had some extra RO tubing laying around so it was an easy fix. I might add getting the tubing out was a lot easier than putting it back in to the rubber seal onto the tube. The quick connect fitting is designed to fit directly to the stem on the control box also. Customer service was quick to respond and said they have tested up to 30 feet of line from the control box to Tube and it functioned properly. After installation I tested the unit several times in a five gallon bucket and it functioned as it should. The supplied neodymium magnet is plenty strong to hold the tube and what ever else you have hooked to it depending on which bracket you choose. I just have the two slot. One that holds the tube and one that holds the top off water line. I went with the diaphragm pump and am pleased with its functionality… It is a little loud inside the cabinet though. I made a silicone gasket to go between the cabinet wall and the pump. This helped a little bit. I then got a Neoprene case to slide over the pump. This helped tremendously. I cut a small hole in the case for the bolt to go through so I could attach it to the cabinet.. I could have just spent the extra money and bought the peristaltic pump, but wanted to try this pump first because it moves a lot more water. That being said, the pump will more than likely not be running that much. I might add my tank is located in the living room. I could have installed the pump else where far away from the living room but I wanted to keep all the ATO components together. The pump really isn’t super loud though. If the TV was turned up, I doubt you could here it. This is a new build so time will tell, but I think the modifications will fix the noise issue which really isn’t a huge issue. I will probably buy another system identical to it for a back up just in case. That’s just me though. I do that with most components of my system. Over all I am super impressed with the Customer Service at Avast! They are quick to respond to any questions or issues you might have. That in itself means a lot. Happy Reefing. Jeff T.

Cynthia C.
United States

AVAST Auto Top Off Works Great!

So far so good. This is replacing a Hydor model I bought that never worked correctly. I have had good luck thus far with AVAST products!