Osmolator Nano 3152 Auto Top Off

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Introducing the little brother to the Tunze Osmolator, one of the industry’s most trusted automatic water top-off device and BRS Recommended. Designed specifically for smaller aquariums, roughly 50 gallons and under, the Osmolator Nano 3152 is a slimmed down version of the full sized 3155. It includes a processor-based anti-overfill system which turns the pump off if after five minutes of filling the level has still not been reached. The Osmolator Nano includes the control unit, low voltage (6V) pump, power adapter, 3m hose, magnet mount and protective cover.



  • Max Head Height: 7.0 ft
  • Tubing Diameter: 7mm OD | 4mm ID
  • Tubing Length: 2 Meters
  • Magnetic holder for sensors up to 10mm or .39"

If you need a pump rated for higher head pressure, check out Tunze's Turbelle High Jet Pump designed to replace the stock osmolator pump


PDF LogoOwners Manual

More Information
UPC 4025167315213
Dimensions (Pump) 4"L x 2" Diameter, (Magnet) 2-1/8" Diameter
Max Tank Thickness 3/8 in.
Included Mounting Magnetic
Control Type Preset Plug & Play (No Controls)
Pump Included Yes
Pump Model Tunze 5000.020 Metering Pump
Warranty 2 Years
Additional Notes For aquariums 55 gallons and under
Water Level Detection Float Valve or Switch
Safety Features Overflow Timer, Run-Dry Protection
Max Head Height 5 -10 Feet
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Product Questions

What is the diameter of the magnetic mount?
Question by: Cindy Thorlton on Mar 6, 2023, 9:50 AM
The magnet is just a hair under 2 1/8".
Answer by: Ash (BRS Staff) on Apr 21, 2023, 1:40 PM
I am planning to use this on an IM15 next to my bed. I’ve heard it can be somewhat noisy for this application.
First question, how loud is it? Would it be disturbing while sleeping?
Second question, could I put it on a timer so it would only have power during the day so it wouldn’t come on while I’m sleeping?
Question by: Paul Zelenski on Jan 3, 2023, 9:04 PM
It is a bit loud when in operation, but only during the time that it is actively filling the evaporated water. You can definitely put a timer on it to only operate during certain hours.
Answer by: William Reed (BRS Staff) on Jan 12, 2023, 1:43 PM
Will this work on a 40b rimmed tank? Will the water level be at or below the rim?
Question by: Chris on Nov 20, 2022, 1:38 PM
Thanks for reaching out! You should be able to use this on all tanks. You can set the water level accordingly as you have some toggle room with the float sensor.
Answer by: James Johnson (BRS Staff) on Nov 26, 2022, 11:01 AM
Hey BRS - do you know if the sensor pod will fit in the back of a Coral life Biocube? Im running no hood and would like to add this since im loosing about a gallon a day due to my A/C here in sunny south florida. Reading the previous question, is the same true for the 3155?
Question by: Chris on Sep 16, 2019, 10:56 AM
Hey there!

They will both be able to fit back there.

Take care
Answer by: Thomas Billington on Sep 16, 2019, 1:33 PM
Just to be safe what are the pump dimensions.
Question by: Johnathan Lebsock on Aug 25, 2019, 10:03 AM
Hey there,
Thank you for reaching out to us. The pump is approximately 4"x2".

Please let us know if you need anything further and take care!
Answer by: Matt Lucero on Aug 26, 2019, 3:28 PM
I'm going to be using the solenoid option with the 3155. Can i purchase it with out the pump it comes with? seam like a waste of money if I'm not going to be able to use it.
Question by: jamie scoli on Nov 9, 2017, 7:00 PM
The Tunze Osmolator only comes with the pump in a single package. You may be able to pick one up used if you are looking for one without a pump, but in all honesty, it is a 20 dollar pump and really doesn't add much extra cost to the 3155 ATO unit.
Answer by: Charlie on Nov 25, 2017, 10:25 AM
Will this work on a 70 gallon setup!
Question by: Thomas Guarino on May 15, 2017, 9:46 PM
Hey there,
While it may be sufficient for a tank of that size, depending on head height the pump has to push against, it does have more limited capacity and safeties set up for small tanks, so we don't generally recommend this one for tanks over 50 gallons.

Have a great day!
Answer by: Zack on May 17, 2017, 4:32 PM
what if you dont have a sump, can you put the controllers directly in the aquarium?
Question by: val sammut on Jan 12, 2017, 12:15 PM
Great question! Yes you can mount the sensors directly in the aquarium. However you may have an issue with keeping the sensor stable if there is a lot of surface agitation in the tank. :-)
Answer by: Randy on Jan 12, 2017, 2:18 PM
If this pump were to break could you use the Apex Neptune PMUP as a replacement for this system?
Question by: Sean on Dec 21, 2016, 1:24 AM
Great question! This pump cannot be used with the Tunze ATO system. The Tunze utility pump is proprietary to their ATO controller and must be replaced with their brand pump. :-)
Answer by: Randy on Dec 21, 2016, 4:17 PM
Can you increase/decrease the pump flow like the 3155?
Question by: Eric Finney on Dec 4, 2016, 8:18 PM
Great question! You cannot make any adjustments to the Nano Osmolator. :-)
Answer by: Randy on Dec 17, 2016, 7:57 AM
I was curious if this auto top off will work for my Innovative Marine NUVO 10. Would the water get too salty by the time the ATO kicks on?
Question by: Trenton on Jul 7, 2016, 12:21 PM
Hi Trenton,
That is a valid concern and if you are keeping SPS in the 10 gallon then we would suggest looking into the Osmolator 3155, however for most fish, and other corals like softies and LPS the Osmolator nano will work just fine. Since the return pump compartment is much smaller than larger tanks, when water evaporates it will move the water level pretty quickly and activate the float switch which is pretty sensitive.
Answer by: Charlie on Jul 7, 2016, 12:42 PM
Does this model have an optical sensor such as the one in the larger model?
Question by: Tristan B on May 4, 2016, 2:47 AM
The Nano will not come with an optical eye. Only the standard float switch. Feel free to let us know if you have any further questions!
Answer by: Connor on May 4, 2016, 2:01 PM
How much travel between on and off with this sensor? 1/3"/ 1/2" etc.?
Question by: Scott butcher on Jan 18, 2016, 10:13 PM
Great question!
The distance between the float being triggered and off is between 1/4" to 1/3" Feel free to let us know if you have any further questions!
Answer by: Connor on Jan 27, 2016, 2:17 PM
I recently purchased one of these and think I will LOVE it but have a question. Each time I have gone to check on it, it seems the relay/sensor (whatever we call it) has shifted slightly so it is no longer sitting level. This is help on with the magnets, so am curious as to why this is happening or what I can do to stop it!
Question by: Wendy on May 18, 2015, 12:54 PM
Great Question,
You can always try implementing a large magnet to ensure the hold is stronger. Other than that, there are some more permanent applications such as small amount of super glue. In any case your best bet will be to contact TUNZE and see if they have any tips or tricks.

Tunze – 512-833-7546 tunze@sbcglobal.net
Answer by: Connor on May 18, 2015, 7:15 PM
Other than the reservoir, What else is needed for this kit? Also, what is the maximum head height of the pump? Thanks !
Question by: Joe on Feb 25, 2014, 12:58 PM
Hi Joe,
Other then the container the kit really comes with everything you need to get started. The pump has a max head height of about 7ft.
Answer by: Bulk Reef Supply on Feb 25, 2014, 12:58 PM
Hey brs,
What's the main differences between the nano and the 3155? Also, would be possible to upgrade in the future without having to buy the whole thing?

Question by: Matt on Dec 16, 2013, 4:29 AM
Hi Matt,
The nano osmolator is just a simple float switch and that is it. The 3155 has the dual level control with the optical eye for primary control and the float switch emergency backup. The 3155 offers superior redundancy.

It would not be possible to upgrade, they are entirely different units.
Answer by: Bulk Reef Supply on Dec 16, 2013, 4:29 AM