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Can an aquarium top-off add glass thickness and a backup?

TUNZE Osmolator 3 supports sensor mounting up to 15 mm with a backup sensor; the nano supports up to 12 mm without one.

No backup can assure overflow prevention. Follow installation and maintenance instructions.

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With no preferences selected: Smart ATO Nano G2 is one option to compare.

No hands-on testingMethod and sources

Smart ATO Nano G2 · first with a product link

Model / item: SATO-276D
  • Sensor mount limit: 12.7 mm.
  • Backup sensor: Yes.
What to note:

Not listed by the maker: maximum pump head.

View at AquaCave

If you choose At least 15.875 mm for sensor mount limit, the first option with a product link becomes ATO Auto Top Off Refilling System 360P.

10 models compared; 10 have a product-page link.

The picks

5 options to compare

Compare the details that matter to your setup.

An option to compare

Smart ATO Nano G2

Sensor mount limit: 12.7 mm.

Model / item: SATO-276D

Key details

  • Backup sensor: Yes.

What to note

Not listed by the maker: maximum pump head.

Sensor mount limit: 12.7 mmSensor technology: OpticalBackup sensor: Yes
See all 4 specs
Sensor mount limit12.7 mm
Sensor technologyOptical
Backup sensorYes
Maximum pump headNot listed by the maker

3 of 4 specs available · source checked September 28, 2026 · Source ↗
AquaCave · Product page checked September 28, 2026

View at AquaCave
Sensor mount limit: At least 15.875 mm

ATO Auto Top Off Refilling System 360P

Sensor mount limit: 20 mm.

Model / item: FZ-ATO-360P

Key details

  • Backup sensor: Yes.

What to note

Maximum pump head: 2 m.

Sensor mount limit: 20 mmSensor technology: OpticalBackup sensor: Yes
See all 4 specs
Sensor mount limit20 mm
Sensor technologyOptical
Backup sensorYes
Maximum pump head2 m

4 of 4 specs available · source checked September 28, 2026 · Source ↗
Fzone · Product page checked September 28, 2026

View at Fzone
Sensor technology: Conductivity

ReefATO+ Auto Top Off System

Sensor mount limit: 12 mm.

Key details

  • Sensor technology: Conductivity.

What to note

Not listed by the maker: backup sensor.

Sensor mount limit: 12 mmSensor technology: ConductivityMaximum pump head: 2.5 m
See all 4 specs
Sensor mount limit12 mm
Sensor technologyConductivity
Maximum pump head2.5 m
Backup sensorNot listed by the maker

3 of 4 specs available · source checked September 28, 2026 · Source ↗
Bulk Reef Supply · Product page checked September 28, 2026

View at Bulk Reef Supply
Also compare 4

Auto Top Off with Controller 580P

Sensor technology: Optical.

Model / item: FZ-ATO-580P

Key details

  • Maximum pump head: 2 m.

What to note

Not listed by the maker: sensor mount limit.

Sensor technology: OpticalBackup sensor: YesMaximum pump head: 2 m
See all 4 specs
Sensor technologyOptical
Backup sensorYes
Maximum pump head2 m
Sensor mount limitNot listed by the maker

3 of 4 specs available · source checked September 28, 2026 · Source ↗
Fzone · Product page checked September 28, 2026

View at Fzone
Also compare 5

Auto Top-Off Kit Version 2

Sensor mount limit: 6.35 mm.

Model / item: ATKv2

Key details

  • Backup sensor: Yes.

What to note

Not listed by the maker: maximum pump head.

Sensor mount limit: 6.35 mmSensor technology: OpticalBackup sensor: Yes
See all 4 specs
Sensor mount limit6.35 mm
Sensor technologyOptical
Backup sensorYes
Maximum pump headNot listed by the maker

3 of 4 specs available · source checked September 28, 2026 · Source ↗
Neptune Systems · Product page checked September 28, 2026

View at Neptune Systems

Comparing Smart ATO Nano G2 · ATO Auto Top Off Refilling System 360P

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The facts that differ

Choose up to three models to compare side by side.

2 identical specs shown. Details that do not apply to these models are omitted.

Published specification comparison
SpecSmart ATO Nano G2Model / item: SATO-276DNo preferences selected.ATO Auto Top Off Refilling System 360PModel / item: FZ-ATO-360PNo preferences selected.
Sensor mount limit12.7 mm20 mm
Sensor technologyOpticalOptical
Backup sensorYesYes
Maximum pump headNot listed by the maker2 m

Smart ATO Nano G2

Model / item: SATO-276D

No preferences selected.

Sensor mount limit
12.7 mm
Sensor technology
Optical
Backup sensor
Yes
Maximum pump head
Not listed by the maker

ATO Auto Top Off Refilling System 360P

Model / item: FZ-ATO-360P

No preferences selected.

Sensor mount limit
20 mm
Sensor technology
Optical
Backup sensor
Yes
Maximum pump head
2 m

Smart ATO Nano G2

View at AquaCave

ATO Auto Top Off Refilling System 360P

View at Fzone

Compare all 10 models

— = no verified listing yet. The published order is independent of links.

All models and their decision specs
ProductHow it comparesKey specCompareAction
Smart ATO Nano G2
Sensor mount limit: 12.7 mm; Backup sensor: Yes.
Model / item: SATO-276D		Sensor mount limit: 12.7 mmView at AquaCave
ATO Auto Top Off Refilling System 360P
Compared with Smart ATO Nano G2: sensor mount limit, 20 mm vs 12.7 mm.
Model / item: FZ-ATO-360P		Sensor mount limit: 20 mmView at Fzone
Auto Top Off with Controller 580P
Compared with ReefATO+ Auto Top Off System: sensor technology, Optical vs Conductivity.
Model / item: FZ-ATO-580P		Sensor technology: OpticalView at Fzone
Auto Top-Off Kit Version 2
Compared with Smart ATO Nano G2: sensor mount limit, 6.35 mm vs 12.7 mm.
Model / item: ATKv2		Sensor mount limit: 6.35 mmView at Neptune Systems
ReefATO+ Auto Top Off System
Compared with Smart ATO Nano G2: sensor mount limit, 12 mm vs 12.7 mm.
Sensor mount limit: 12 mmView at Bulk Reef Supply
ReefBreeders ATO
Compared with Smart ATO Nano G2: sensor mount limit, 15.875 mm vs 12.7 mm.
Model / item: RBATO		Sensor mount limit: 15.875 mmView at ReefBreeders
Osmolator 3
Compared with Smart ATO Nano G2: sensor mount limit, 15 mm vs 12.7 mm.
Model / item: 3154.000		Sensor mount limit: 15 mmView at TUNZE
Smart ATO Nano G2
Sensor mount limit: 12.7 mm; Backup sensor: Yes.
Model / item: SATO-276D
Sensor mount limit: 12.7 mm
View at AquaCave
ATO Auto Top Off Refilling System 360P
Compared with Smart ATO Nano G2: sensor mount limit, 20 mm vs 12.7 mm.
Model / item: FZ-ATO-360P
Sensor mount limit: 20 mm
View at Fzone
Auto Top Off with Controller 580P
Compared with ReefATO+ Auto Top Off System: sensor technology, Optical vs Conductivity.
Model / item: FZ-ATO-580P
Sensor technology: Optical
View at Fzone
Auto Top-Off Kit Version 2
Compared with Smart ATO Nano G2: sensor mount limit, 6.35 mm vs 12.7 mm.
Model / item: ATKv2
Sensor mount limit: 6.35 mm
View at Neptune Systems
ReefATO+ Auto Top Off System
Compared with Smart ATO Nano G2: sensor mount limit, 12 mm vs 12.7 mm.
Sensor mount limit: 12 mm
View at Bulk Reef Supply
ReefBreeders ATO
Compared with Smart ATO Nano G2: sensor mount limit, 15.875 mm vs 12.7 mm.
Model / item: RBATO
Sensor mount limit: 15.875 mm
View at ReefBreeders
Osmolator 3
Compared with Smart ATO Nano G2: sensor mount limit, 15 mm vs 12.7 mm.
Model / item: 3154.000
Sensor mount limit: 15 mm
View at TUNZE
10 catalog models

How the comparison works

Your choices are compared with each model’s product details. A missing or conflicting value stays unknown and cannot satisfy a choice you select. The starting order helps you browse; it does not rate real-world performance.

Source dates appear with each link below. A source date does not confirm today's price or stock.

Finder methodologyReport a correction
Sources for all 10 models

Fit the sensor before choosing its technology

Sensor-mount limits run from 6.35 to 20 mm among the systems with a known limit. Red Sea uses conductivity sensing and accepts a sensor mount up to 12 mm; ReefBreeders ATO uses optical sensing. Red Sea's system is restricted to seawater, so its sensing method is not a freshwater alternative.

Measure the mounting surface. Inspect the whole installation: a sensor bracket's limit does not cover a separate controller holder, tank rim, cable reach or tubing route. Our comparison reads maker mounting and sensing details without operating the refill systems.

Separate overflow backup from pump lift

TUNZE Osmolator 3 has backup sensing, while Osmolator 3 nano does not have a second sensor. An unknown backup value means the source did not settle that detail; it does not mean the system lacks every protective feature. Follow the maintenance instructions regardless of the backup design.

Maker maximum pump-head figures span 2 to 6.2 m where available. Those limits do not describe the flow you will get at your installation height, and discharge head cannot stand in for suction height. Plan pump placement and the reservoir route separately from sensor fit.

Before you buy

Does the glass thickness check guarantee installation fit?

It checks the sensor mount only. Check rim clearance, cable reach, tubing position, pump placement, and any separate controller bracket. AutoAqua Nano G2 has a 12.7 mm sensor limit but a 3 to 10 mm controller holder.

Does a backup sensor guarantee that a tank cannot overflow?

This field only records whether an additional water-level sensor is documented. It does not certify reliability or replace the installation and maintenance instructions.

Why are some pump head values blank?

The manufacturer page did not provide an unambiguous maximum discharge head. AutoAqua Nano G2 lists suction height, which is a different measurement, so it is not substituted here.

Can you use any top-off system in freshwater?

Red Sea ReefATO+ is for seawater only. A water-level sensor type does not establish freshwater suitability. AutoAqua Nano G2 also has a separate controller-holder limit; use the exact installation instructions for every component. TUNZE Osmolator 3 supports sensor mounting up to 15 mm with a backup sensor; the nano supports up to 12 mm without one. The mounting limit changes too. Osmolator 3 suits thicker glass within its limit if you want the additional sensor, but no backup guarantees overflow prevention. Follow installation and maintenance instructions; other mounting clearances still matter.