Osmolator Nano 3152 Auto Top Off - Tunze

Tunze Osmolator Nano 3152 ATO
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  • Tunze Osmolator Nano 3152 ATO
  • Tunze Osmolator Nano 3152 ATO Floats
  • Tunze Osmolator Nano 3152 ATO Pump
  • Tunze Osmolator Nano 3152 ATO Included Parts
  • Tunze Osmolator Nano 3152 ATO Magnets
  • Tunze Osmolator Nano 3152 ATO Power Supply
  • Tunze Osmolator Nano 3152 ATO Box

Osmolator Nano 3152 Auto Top Off - Tunze

77% Recommend this to a friend (63 of 82)

SKU: 202331

reg. $99.37

Special Price: $84.46

In Stock: 140
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Quick Overview

The Tunze Osmolator Nano 3152 Auto Top Off is designed for smaller tanks, approximately 50 gallons and under. One of the safest ATO’s available. Utilizes an single sensor to monitor water levels and a controller that protects against overdosing.

Magnetic holder for sensors up to 10mm or .39".

Max Head Height: 7.0 ft


Full Details

Owners Manual



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.


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  • Working great By Donald on 11/9/2017

    One less thing I have to deal with each day! My water level stays constant so salinity is constant as well. This is being monitored by my Apex using leak detection module.

    I am very pleased with how well things are working.
  • Does not work consistently. By Zhong on 11/7/2017

    The first one I bought 4 years ago is the only one that ever worked. I have bought 4 of these. I wonder if they changed manufacturers or quality of parts. The sensor will work for the first time the water level is low. Once it stops, the sensor will not pick up the low water level again until you unplug the system from the electric sort and plug it in again. The pump will constantly turn on and off even when it is not pumping.
  • Major issues By Morgan on 10/20/2017

    I currently have 2 of these. Only one is in working condition. One's on a biocube 29 and One's on a 30 standard. Both units have failed. I had a pump burn out on one unit. Bought a replacement pump. On the other unit the float sensor just wont work. I can hear the pump power up when i plug it in but it wont pump water. I have purchased 3 of the oz minis over 4 years. The last failure was the small circuit board where you plug in power got so hot it melted the plastic housing. You could smell electrical burn in the whole house. Of course it was in the 26th month of ownership. I will never buy another product by Tunze.
  • Good unit if you only need it for a year :) By KR on 10/6/2017

    I did not have the plug unplug issue but I do think the default fail safe it comes programmed with is pretty dang conservative so I'm not surprised people have that issue. I have had this unit for about 2 years and it worked great for a year and a half then the pump stopped working one day and that was that. I'm sure it's under warranty but their warranty process is a pain plus I should bite the bullet and upgrade to a better system.
  • Same problem... By Chris on 8/3/2017

    The sensor will shut off the pump but will not turn the pump on. I have to cycle power for the pump to work.
  • 1 is a yay the other a nay By Bloatedguppy on 7/31/2017

    Bought 2 of these, 1 works as intended, the other requires the same unplug then plug it back in to work every time defect after a week.
  • Works great By Ken on 7/26/2017

    Great product. Works as described. No problems. Reliable so far.
  • I have three for all three of my tanks and love them! By Kurt on 7/19/2017

    I love these! I use one on each of my tanks and I have three tanks total. I haven't had any problems with them. When installed correctly they work perfectly. Read the instructions and follow them. It's got a build in fail safe system that gives you a peace of mind.

    I see some bad reviews on here of people saying they have to unplug and replug in the power cord to get the ATO to work. This is a failsafe built into the device. If the pump runs longer than a couple minutes it has to be reset. If the float value gets stuck it won't keep pumping and pumping and either flood the inside of your stand and totally throw off your salinity. Something must be causing you float value to become stuck. I have three of these and that’s not a common problem.
  • Didn't last. By Ronald on 7/7/2017

    Worked perfect for a year and a half. Then one day I noticed it wasn't topping off. Unplugging and resetting worked for a few days then it quit working completely. My 3155 is still going strong and is much older.
  • The first month it worked great......then it started having the same problems of several others that have posted. I unplug it and then plug it back in and it turns on......works for 2-3 days and starts the same process all over again. A $100.00 waste. By John on 7/2/2017

    Again........first month it worked great.......then it stopped working. Had to continually unplug and re-plug to get it to come on... Quite a few others have had the same problem.......$100.00 wasted and to help from anyone. What a messed up system.
  • The standard for smaller tanks By Join the Revolution on 5/11/2017

    Tunze quality on a smaller package. These are bullet proof top off units. Those who have problems are not reading the instructions and have it installed in an incorrect area. You get a two year warranty on this brand. Who else does that? Nobody.
  • Great simple solution for top off By Todd on 5/5/2017

    I've used this top off system for over 2 years now. I never have any issues with it.

    Most of the complaints I see people are mentioning they have to unplug it and plug it back in.

    This is actually a feature to prevent a disaster. If the pump runs longer than 3 minutes it has to be reset. Under normal operation this never occurs. However if the sensor were to get stuck this feature would prevent the system from pumping until it was out of water. Normally mine only runs for less than 10 seconds at a time.

    The other procedure that requires you to unplug it is when your reservoir runs dry. I assume this is to prevent the pump from burning out.

    An on/off switch would be nice to make these "reboots" easier, but it's not much of a hassle to take the plug out for a second or two.


Ask a question

Product Questions

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 4:29:00 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 4:29:00 AM
what if you dont have a sump, can you put the controllers directly in the aquarium?
Question by: val sammut on Jan 12, 2017 12:15:00 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 (Admin) on Jan 12, 2017 2:18:00 PM
Will this work on a 70 gallon setup!
Question by: Thomas Guarino on May 15, 2017 9:46:00 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 (Admin) on May 17, 2017 4:32:00 PM
Can you increase/decrease the pump flow like the 3155?
Question by: Eric Finney on Dec 4, 2016 8:18:00 PM
Great question! You cannot make any adjustments to the Nano Osmolator. :-)
Answer by: Randy (Admin) on Dec 17, 2016 7:57:00 AM
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 12:58:00 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 12:58:00 PM
How much travel between on and off with this sensor? 1/3"/ 1/2" etc.?
Question by: Scott butcher on Jan 18, 2016 10:13:00 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 (Admin) on Jan 27, 2016 2:17:00 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 12:54:00 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 (Admin) on May 18, 2015 7:15:00 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 1:24:00 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 (Admin) on Dec 21, 2016 4:17:00 PM
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 12:21:00 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 (Admin) on Jul 7, 2016 12:42:00 PM
Does this model have an optical sensor such as the one in the larger model?
Question by: Tristan B on May 4, 2016 2:47:00 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 (Admin) on May 4, 2016 2:01:00 PM
Why can't this model be used on a larger system?
Question by: Clayton on Aug 29, 2013 3:36:00 PM
Hi Clayton,
The unit is not suited to large aquariums because it has a timer based cut off so the pump will only run for a short period of time. Using it with a large tank can result in the the pump turning off before its finished replacing the evaporation.
Answer by: Bulk Reef Supply on Aug 29, 2013 3:36:00 PM