XP Aqua Duetto2 ATO

Hands-off, rock-steady water level. The XP Aqua Duetto 2 is the world's smallest dual-sensor auto top-off, a complete plug-and-play system that automatically replaces evaporated water to keep your water level and salinity stable. Its proprietary dual-optical sensor packs a primary and a backup sensor into one tiny housing, working with intelligent QST programming to prevent overfilling. Everything you need is included, and a magnetic coupling makes mounting the sensor take seconds. For AIO and nano tanks without a sump, see the Sumpless ATO2.

Key Features

• World's smallest dual-optical sensor: a primary level sensor plus a secondary backup
• Intelligent QST programming with two layers of overfill protection
• Complete kit with a quiet 74 gph DC pump, tubing, and mounting hardware
• Magnetic coupling for tool-free sensor mounting on glass up to 1/2 inch
• Plug-and-play, with no programming or calibration required
• Works on both freshwater and saltwater aquariums

Specifications

Setup

• Mount the sensor at your target water level using the magnetic coupling
• Place the pump in your RO/DI top-off reservoir and run the tubing to the tank
• Plug it in; it tops off automatically when the level drops and stops at the set point
• Use RO/DI or fresh top-off water only, never saltwater, since an ATO replaces evaporation and not salt

Pair It With

• XP Aqua Sumpless ATO2 for AIO and nano tanks without a sump
• AutoAqua Smart ATO Nano G2 for a simpler single-sensor option
• AutoAqua Inline TDS Meter to keep an eye on your RO/DI water quality
• Browse more water care

Frequently Asked Questions

What does an auto top-off do?
It automatically replaces water lost to evaporation, so your water level and salinity stay stable and you do not have to top off by hand.

Freshwater or saltwater?
Both. Stable water level benefits any tank, and it is especially valuable on reef tanks where evaporation shifts salinity.

Do I fill the reservoir with fresh or salt water?
Fresh RO/DI water only. Evaporation leaves salt behind, so topping off with saltwater would steadily raise your salinity.

What happens if a sensor fails?
The dual-optical sensor and QST programming provide two layers of protection: the backup sensor shuts the pump off if the primary has an issue, preventing an overfill.