Tunze Osmolator Universal 3155 Auto Top Off

Tunze Osmolator Universal 3155 Auto Top Off
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  • Tunze Osmolator Universal 3155 Auto Top Off
  • Tunze Osmolator 3155

Tunze Osmolator Universal 3155 Auto Top Off

97% Recommend this to a friend (255 of 263)

SKU: 202307

reg. $209.99

Special Price: $146.99

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Quick Overview

Why does BRS recommend this?

Bulk Reef Supply tried many different water level switches and auto top off solutions before giving the Tunze 3155 Osmolater Universal Auto Top Off BRS Recommended status. Despite its higher price this is by far our favorite solution. Spending the extra money on a Tunze Osmolater will give you that extra peace of mind and insurance from having a disaster that ruins carpets or hard wood floors.  For the value, and reliability it is hard to beat.


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Product Questions

I have a litermeter 3 that has failed. It pushes water about 30 feet from the litermeter to a sump tank. Will this pump do the same?
Question by: Spencer on Apr 29, 2014 12:54:00 PM
Hi Spencer,
The max head pressure on the included pump is about 7ft. It likely wouldn't be well suited to this application. That said though, you can get the additional switch socket adapter which would allow you to control any pump via the osmolator system. That way you can use a pump that can handle the head pressure.
Answer by: Bulk Reef Supply on Apr 29, 2014 12:54:00 PM
If i have a wave maker and this ATO in the same tank (I don't have a sump), would the waves cause the pump to turn on and off constantly? Thanks
Question by: Christian on Jul 17, 2014 9:40:00 PM
Hi Christian,
In theory it could present a problem but the circuitry in the Osmolator should help to prevent that. Every time the ATO is triggered it runs for a minimum of 15 seconds. It adds overfill to prevent short cycling. In most cases this should be sufficient unless the height of your waves is constantly changing.
Answer by: Bulk Reef Supply on Jul 17, 2014 9:40:00 PM
How much head will the pump push
Question by: Jeff on Nov 28, 2013 2:50:00 PM
Hey Jeff,
The pump on the osmolator has a max head height of 7ft.
Answer by: Bulk Reef Supply on Nov 28, 2013 2:50:00 PM
What is the measurement on the pump, as in the widest part? I need to know if it will fit in my container I plan to buy.
Question by: David Price on Jul 7, 2015 12:10:00 PM
Hey David,
The diameter of the pump is just under 2" this is how wide the cap will need to be in order to allow the pump to pass through.
Answer by: Connor (Admin) on Jul 7, 2015 1:03:00 PM
Will this work with the Apex controller?
Question by: Jim on Aug 3, 2014 11:31:00 AM
Hi Jim,
The Tunze Osmolator is an entirely self sufficient system. It is perfectly fine to connect the Osmolator to one of the Apex's power outlets incase you wanted to cut the power for some reason (like when you are doing a water change) though the Apex isn't capable of reading the Osmolator's sensors or anything of that sort.
Answer by: Bulk Reef Supply on Aug 3, 2014 11:31:00 AM
Would you happen to know the max head pressure of the Tunze Osmolator's pump?
Question by: David on May 10, 2014 11:50:00 PM
Hi David,
The max head pressure on the osmolator pump is 7ft.
Answer by: Bulk Reef Supply on May 10, 2014 11:50:00 PM
what pump do you suggest to go with the3155 osmolator?
Question by: BILL on Nov 13, 2013 7:37:00 AM
Hey Bill,
The Osmolator actually comes with the pump right in the package so you don't need to buy one!
Answer by: Bulk Reef Supply on Nov 13, 2013 7:37:00 AM
Just wondering if I need 2 ATO. I know you can place it either in the sump or in the tank, but my question is if I place it in the sump will it also refill my tank in that process. I don't see that happening but if it does please let me know.
Question by: Ronald on Jan 13, 2014 2:32:00 AM
Hi Ronald,
If you have a sump, it MUST go in the sump, in the chamber where your return pump is. This is the only area of your tank that will have a changing water level depending on evaporation (unless its far too late!). Only one ATO would be necessary but it must go in that location if you have a sump.
Answer by: Bulk Reef Supply on Jan 13, 2014 2:32:00 AM
My Tunze Osmolator ATO keeps getting stuck in the ON position. I soaked the electronic eye in vinegar and it was fine for a week, but then it stuck on again. Do these electronic eyes fail after many years of use? I've been using it for about 4 years. Is there any way to replace the eye without having to buy a whole new system?

Daire Fontaine
Question by: Daire Fontaine on Jan 17, 2014 12:23:00 AM
Hi Daire,
We run into very few issues with these but after that length of time I would imagine its possible for any component to fail. We don't have individual parts like the optical eye, but if you give Roger and company a shout over at Tunze USA, he might. At the very least he could likely help you narrow down exactly what it is. The number I have for them is 512-833-7546 tunze@sbcglobal.net
Answer by: Bulk Reef Supply on Jan 17, 2014 12:23:00 AM
Does the pump get placed directly in the top off water reservoir? If so what are the dimensions of that pump? I am trying to decide what kind of reservoir I can use before purchasing a ATO.
Question by: Mark on Jun 5, 2014 8:39:00 AM
Hey Mark,
That is correct. Its a submersible pump that gets stuck right into the top off water. If your interested in this ATO system you should give this blog article a quick read. It goes into a lot more detail on the system (which is one of my favorites).


Answer by: Bulk Reef Supply on Jun 5, 2014 8:39:00 AM

Full Details

The Tunze Osmolator 3155 is one of the safest ATO’s available. It utilizes an electronic eye sensor to monitor water levels and a backup float switch sensor with an optional audible alarm. The controller protects the quiet metering pump from running dry and reports an empty storage tank. Two magnetic holders for sensors and multiple mounting brackets included as well as a pump.

LED indicator lights the Osmolator will allow you to visually see if their are any issues with your top off system. 

Two technologies of water level monitoring, and built in safety back-ups.

The optical eye sensor will keep the water level very steady to keep the salinity from fluctuating in your aquarium.  The Osmolator does work well with kalkwasser.  



Note: With any pump, kalkwasser can cause premature wear.  New pumps are available at a very reasonable price. 

Replacement Metering Pump



Click Here



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  • Worth Every Penny! By Chris on 11/19/2015

    Easy to set up and install. Totally worth not having to add water to my tank everyday. All i have to do is keep an eye on my ATO reservoir and refill it once a week. Definitely one of the smartest purchases i have made for my reef tank!
  • Love the system, Pump is a bit noisy By Nicole on 11/12/2015

    Just put this in my FW tank since the boyfriend hates the sound of running water and I hate hauling buckets every couple weeks to prevent that noise. Awesome that I can connect a separate pump instead of the original if I feel like it ( I won't, too broke now). I plan on getting another for my future saltwater tank.
  • Sweet By Kurtis on 11/9/2015

    This top off is awesome to say the least, very easy set up and works great. Alarms great feature and the control unit is user friendly. Only issue is the system is on the pricy side, but very happy with it. Everybody needs one.
  • Love By JOE on 11/9/2015

    I've had this pump for maybe close to a year on my 150 gallon and i couldn't be happier the the setup is easy and i have never had one issue with this thing love it compared to my jbj ato on my 90g.
  • 1.5 years of operation, still like its out of the box!! By Devin on 11/6/2015

    This ATO is amazing! it functions so well, and is so user friendly! over 1.5 years of operation and ZERO issues!!! I do replace the pump every 8-12 months just in case, but have yet had one fail on me!
  • Awesome Product By Martin on 11/6/2015

    Worth every penny. Excellent quality and performance. Simple to install and very adaptable.
  • Works ok By Steve on 11/2/2015

    I've had this running for about week now and for whatever reason it is filling up too high at times and setting off the alarm. The small pump is also incredibly loud. It's irritating when it's turning on every 10 minutes. I expected better all around performance for a ATO at this price range.
  • Excellent product! By Tony on 10/30/2015

    You can't go wrong with this ATO!
  • Love It By David on 10/30/2015

    This is truly one of the best top offs i have seen the piece of mind is all i care about love the fact it has 2 ways it monitors. Love the fact it has a alarm when it goes to high and shuts its self off, a bit pricey. You get what you pay for, i had another one that the switch would get stuck and start running and running until pulled it down. This is a must buy if you want piece of mind when your not around
  • Piece of mind, stable salinity By Adam on 9/15/2015

    Wow, what a great purchase. This is the way to keep your tank topped off for evaporation loss and keep salinity EXTREMELY stable. Drop dead simple with two forms of measuring water needed. Takes about 5 minutes to install and get running. This is especially helpful when I travel and have a sitter care for the tank. All they have to do for water is keep the top off jug full and everything else from a water level perspective is covered. I really love this product. This is the best solution for automated top off I have seen.
  • Love it By Jorsreeftank on 9/6/2015

    This is my third ATO system so I feel qualified to Say this is the best one. It's easy to install an what I like best is its safety redundancy and the fact that it really keeps my water where I wantbit!! It kicks the pump on as soon as the level drops. I would say less than a pint
  • Best ATO By Joesreeftank on 8/23/2015

    Do not screw around with the others, This one does what it says, It keeps my Sump right were I set it, I have a 40 gal sump and if it looses less than a couple of pints it kicks on and tops off..Easy to install

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