Mon-Thurs 7am-5pm PST
Fri 7am-4pm PST

Questions about products, orders, shipping?
Contact us by call or email


XP Aqua Ultimate ATO - Complete 4-Sensor Aquarium Auto-Top-Off System

$199.99 $169.99Save: $30.00 (15%)

Item #: 0X1856

Ships Free!

Only 2 left - order now!

In Stock

XP Aqua Ultimate ATO - Complete 4-Sensor Aquarium Auto-Top-Off System

Why Choose Ultimate ATO?

With 2 X dual-optical sensors, the Ultimate ATO is the first ATO to include 4 sensors. The 4 sensors allow us to design a dual-stage overfill alarm that is less intrusive as well as a run-dry protection feature that prevents your sump from running dry: which is also a first. The Ultimate ATO’s versatility is also unmatched. An efficient DC pump is included for a standard installation. If you require a larger ATO pump for a remote sump installation, a Socket Switch is included that allows you to run a pump up to 10A (1000W). A solenoid valve is also included for aquariums that are topped off directly with an RO/DI system. We designed the Ultimate ATO to offer you the ultimate protection with the ultimate convenience!


  • World’s first 4-sensor ATO
  • One sensor for top-off detection
  • Two sensors dual-stage overfill alarm w/ QST Programming
  • One sensor for run-dry protection (also a first)
  • Versatile installation with accessories included
  • Efficient DC Pump – Standard
  • Socket switch for use with AC pumps (up to 10A)
  • Solenoid valve for use with RO/DI systems
  • Super precise water level control
  • Super easy installation; plug-and-play
  • No programming or adjustments required
  • Works in complete darkness 

Technical Details:

  • Model: UATO-400P
  • Max mounting thickness : 1/2" (12.7 mm)
  • Length of Cable between Sensor and Controller : 6 ft (180 cm)
  • Power Adapter: 
    • Power Input : 100~240VAC 50-60HZ
    • Cable Length : 6 ft (180 cm)
  • DC Pump:
    • Max Head : 6.5ft (200cm)
    • Flow Rate : 74 gph (280lph)
    • Power : 4.8 W @ 12 VDC
    • Cable Length : 6 ft (180 cm)
  • RO Solenoid Valve:
    • Power Consumption : 6 W @ 12 VDC 
    • 1/4 inch RO Tubing Connection
    • Cable Length : 4 ft (120 cm)
  • AC Switch:
    • Capacity : 100~240 VAC - 50~60 Hz
    • Max. Load : 10 A / 2400 W @ 240 VAC
    • Cable Length : 10 ft (300 cm)

*Please avoid setting up the sensor in an area with micro bubbles or direct light. 

Manufacturer information

Ever since the ATO systems were invented by Tunze in 1985, they have been helping saltwater reef aquarium hobbyists maintain stable salinity levels and offering a ton of convenience. ATO is short for ‘aquarium top off’ system. It is also called an ATK ‘aquarium top-off kit’, or osmolator / osmo regulator in Europe. Here at XP Aqua, we have combined all the best ATO technologies and added several proprietary features to create the safest and most dependable ATO money can buy! Our micro sized ATO sensor features two precise optical sensors to offer you more protection. Additionally, each XP Aqua ATO system includes our intelligent QST programming to prevent overflows. If you are looking for the best ATO system, check out our awesome line of ATOs!

4 Stars


Reviewed on
November 07, 2020

No, I would not recommend this.


Cons: Fails on on position

Worked well for a few months then I came home to an overfill tank. Thought maybe another piece of equipment was interfering with the sensor so I moved the other piece. Worked well for a week then came home to an overfill tank again. The control unit is not stopping the pump even though the alarm is sounding. Going in the trash. Now have to buy a new ato

Was this review helpful? 1 0


Reviewed on
September 18, 2019

No, I would not recommend this.

Was impressed, but now I'm not so sure!

Pros: Small and easy set up

Cons: No live customer support, just an e-mail

Bought this almost a year ago and it stopped working. It's placed in a secure location away from the sump and all other components and it has a burnt smell. When I have issues I expect help and XPAqua has no live support or 800 number to call and speak to someone. To me as a consumer in this hobby that is very important! I 'll be sending it in hopefully for warranty exchange, but next time I'll check support availability before I buy in combination with product rep.

Was this review helpful? 0 0


Reviewed on
May 13, 2019

Yes, I would recommend this.

Super easy

Pros: Super easy setup

Super easy setup, less than 10 minutes. Dc pump stopped working after a day, but great communication with manufacturer, immediately sending me a replacement. Use the "switch" with a ppwerhead in the meantime and works great.

Was this review helpful? 3 0


Reviewed on
April 25, 2019

Yes, I would recommend this.

Very Nice

Pros: Easy to Setup

Cons: No.

Very nice design no more checking my RO water everyday.

Was this review helpful? 0 0


Reviewed on
September 11, 2018

Yes, I would recommend this.

Nice Product SA Test

Nice Product

Was this review helpful? 0 11


Reviewed on
September 04, 2018

Yes, I would recommend this.

Great ATO

Pros: Easy to Use and Set Up, 4 Sensors, Looks good, Touch sensor button on control

Cons: None so far, no wifi text message for when my ATO bucket is low

I set this up on my tank in literally 10 minutes from start to finish. Very simple to use design and so far the sensors have done there job well. Theres a small tone when theres too much water added. (I learned from me adding water separately to see what happened, not the ATO malfunctioning). The pump it comes with is Tiny but seems to be powerful enough. It comes with an attachment to allow you to add your own pump but I would definitely give the little one a try, it may surprise you. Its got literally one button thats function is easily explained in the instructions manual (Touch sensor with a Boop sound). I plan on buying one for my other tank that's currently ATO-less. (My 3rd tanks has the Tunze osmolator ATO and this one is much easier to understand and set up in comparison) (Instagram: Raiders_Reef)

Was this review helpful? 13 0


Reviewed on
July 17, 2018

Yes, I would recommend this.

Great Product

Love it !!!!

Was this review helpful? 0 15

We use cookies to provide a personalized site experience. By continuing to use & browse this site, you agree to our Privacy Policy.