Osmolator 3 Auto Top Off

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Next-Generation Auto Top Off System

  • Stable Aquarium Salinity Level
  • Plug and Play Convenience
  • Compact All-In-One Design
  • Built-In Safety Features


Tunze has long been recognized for their auto top off systems and like its predecessors, the Osmolator 3 includes everything you need for installation (except ATO reservoir) with no software setup required. 

With its optical and thermal sensors, it ensures precise water level control and protection against overfilling-- all within a compact design. Designed for versatility, it can be placed in the sump's return section or on the aquarium's edge, depending on your setup.


The Optical Sensor

The large, precise optical sensor detects the water level with an accuracy of 0.5mm and is resistant to air bubbles, deposits, and scratches. The independent thermal safety sensor stops the ATO pump in the event of overfilling. The sensor's strong magnet mount is compatible with sumps/aquariums up to 15mm (0.59") thick. The protection cap helps prevent curious critters from reaching the sensor.

The ATO Pump

Each Osmolator 3 comes with a Turbelle High Jet pump to move water from your ATO reservoir to the aquarium or sump. This long-lasting pump has an impressive maximum head height, being able to pump just over 20 feet vertically. Run-dry and blockage protection is built-in.




Max. Glass Thickness (Sensor): 15mm (0.59")

Max. Glass Thickness (Tube Holder): 22mm (0.87")

Max. Delivery Height: 6.2m (20.34')

Tubing Diameter: 6mm OD | 3.9mm ID

Tubing Length: 3m (9.84')


What's Included?

Osmolator 3 Sensor

Magnet Holder

Turbelle High Jet Pump

12V DC Power Supply

Tube and Tube Holder

More Information
UPC 4025167412004
Manuals Osmolator 3 Manual
Pump Included Yes
Pump Model Tunze 5000.020 Metering Pump
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Product Questions

What are the dimensions of the pump itself?
Question by: Christian Thompson on May 9, 2024, 3:59 PM
Dimensions (L x W x H) - 78 x 41 x 41 mm (3.1" x 1.6" x 1.6")
Answer by: Tyler Schafer (BRS Staff) on May 14, 2024, 10:12 AM
Does this ato have a alarm ?
Question by: GARY HASBERRY on Jan 11, 2024, 10:21 PM
Yes, it has an alarm.
Answer by: Laura (BRS Staff) on Feb 8, 2024, 4:46 PM
What is the width and diameter of the sensor housing? I have a nano tank and want to use the new tech but need to know the dimensions to see if it will fit. Thanks
Question by: George Thompson on Dec 20, 2023, 11:40 AM
Hey there,
Thank you for reaching out to us. It is approximately 2.5" circle that is 1.25" thick.

Please let me know if you need anything further and take care!
Answer by: Matt Lucero (BRS Staff) on Feb 15, 2024, 9:53 AM
How long is the wire between the sensor and pump? Is there an extension if the RO source is further away?
Question by: Brett on Dec 7, 2023, 1:28 AM
Hi there, great question. The wire will be 3 meters long and unfortunately there is not an extension cord.
Answer by: Grace (BRS Staff) on Jan 25, 2024, 11:45 AM