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★ Featured in Atlantis

Tunze

Osmolator Nano 3

Name: Tunze Osmolator Nano 3
Brand: Tunze

Flow · ATO

ATO with optical sensor — salinity stability.

Sensor type

Optical (photodiode)

Pump

5W DC dosing pump

Max lift

1.5 m

Tubing

4/6 mm flexible silicone

Power

12V DC, 5W controller + 5W pump

See it in the Atlantis tank build →

Osmolator Nano 3

$127.49 at Bulk Reef Supply

Buy →

Summary

Tunze's compact optical-sensor ATO. Optical (not float) means no mechanical sticking — the photodiode reads water surface refraction. Tiny footprint, suits nano sumps and small builds. Atlantis ran a float-based ATO for 6 months before swapping to this — never went back.

Best forany tank up to 600 L (159 US gal) with a 4-6 L reservoir Mountmagnetic glass clip, sump or tank rim Skill beginner

Tank-size fit (log scale)

50L 100L 200L 400L 800L 1500L

Best-fit range: 4-6 L

★ Atlantis verdict

"Replaced a JBL float ATO at Atlantis Q1 2026. No salinity drift since. Optical sensors are the right call."

See it in the Atlantis tank build →

Full specifications

Sensor type Optical (photodiode)

Pump 5W DC dosing pump

Max lift 1.5 m

Tubing 4/6 mm flexible silicone

Power 12V DC, 5W controller + 5W pump

Mount Magnetic clip up to 12mm glass

Safety 30-sec runtime cutoff per cycle

Warranty 2 years (Tunze EU)

What sells it / What holds it back

✓ Pros

✓ Optical sensor — no stuck float, no mechanical failure mode

✓ 30-second per-cycle cutoff prevents flood-the-tank failures

✓ Tiny footprint vs traditional dual-float ATOs

✓ Tunze long-term parts support

✗ Cons

✗ Optical sensor can get fouled by algae — needs monthly wipe

✗ Reservoir not included — bring your own (4-6 L jug works)

✗ Pump runtime audible (faint whirring) — annoying in living room if not isolated

What's in the box

Optical sensor module
DC pump
Controller + 12V PSU
Silicone tubing (2m)
Magnetic clip + suction cup backup

Pairs with / Replaces

Pairs with

Featured in famous tanks

This piece of gear is in the documented build of 2 tank tours.

★ 60 gal

Project Atlantis

Atlantis Reef Keeping

LPS dominated

700 gal

Tidal Gardens 700-Gallon Coral Farm

Than Thein

Coral propagation / display

Where to buy

Affiliate disclosure. Some links on this page are affiliate links — we may earn a commission when you buy through them, at no extra cost to you. As an Amazon Associate we earn from qualifying purchases. Prices and stock are refreshed nightly from each retailer.

Retailer	Price	Stock	Checked
Bulk Reef SupplyAff bulkreefsupply.com	$127.49	In stock	today	Buy →

Side-by-side compare

	This product Tunze Osmolator Nano 3 $127.49	AutoAqua Smart ATO Mini See site
Sensor type	Optical (photodiode)	Optical (photodiode)
Pump	5W DC dosing pump	4W DC dosing pump (included)
Max lift	1.5 m	1.5 m
Tubing	4/6 mm flexible silicone	4/6 mm silicone
Power	12V DC, 5W controller + 5W pump	12V DC, 4W controller + 4W pump
Mount	Magnetic clip up to 12mm glass	Magnetic clip up to 12mm glass