Ive been using this product for about 6 months now. Has not failed me yet. This is a must have for saltwater tanks, keeps water levels/salinity the same. my only regret is not getting this sooner..

When i eventually get a larger tank ill get the bigger tunze osmolator for sure.

Typical tunze product well built and works like a charm, recommend this to everyone with ATO system

Pros
Compact
Magnet attachment
More than enough for my 29g Biocube
Easy to set up (Except the tube for the pump)
Only runs for 1.8 seconds but can be boosted up for bigger tanks. (No fear of flooding)

Cons
Float has to be Installed PERFECTLY Vertical. Mine got stuck on the first day. Luckily I was in front of the tank. I knocked the sensor and it stopped pumping.
No alarms. The motor will just pulse every 10 secs. You wont hear it unless the room is silent.

Does what its suppose to. If you're on a budget its a good buy. In hindsight wish I would have held out to buy the reg Osmolator with the alarms and laser eye!

This is a great solution, especially for a nano reef. The magnet mounts are strong, and I am confident they will hold in place. The unit itself is tiny, and pretty inconspicuous, even if going into a display tank rather than a sump. The only drawback I see is it is a bit noisy when compared to my other tank, which I use an aqualifter on for the ATO.. but it is not obnoxiously loud.

1 bit of info that might be useful to include in the product description is the diameter of the pump. This could be important depending on the top off container that is used. For my purposes, I used a small potable water container designed for a boat or RV. The biggest opening was 1.75 inches, which I thought would be ok for the pump. Turns out the pump diameter is 1/8" larger, so I had to cut a new hole in the tank using a hole saw. No big deal, but would have been nice to know the size before ordering.

Bought this top off for our 29g tank. Set up took about 5 minutes. Very easy. I really like the back up timer of not letting the pump run for more than 2 minutes. Really assures that im not going to over fill my tank.

ok i got this ato for to do 2 things add kalk and add top off water at same time. i put it on my redsea max 250 that i upgraded with a refugium because the filter and skimmer just dont cut it on this tank so i built a custom sump for it. after i put the tunze top off in the sump i set it up where when it tops off water right where it poors over the last chamber witch caused current to let me know it was keeping it at same lvl. if theres a little water current it will kok the float bobber some what and wont let it drop freely so make sure if you get this to make sure it tops off enough to make less water current are add something to keep current away from float bobber. other then that i found no issues so far with this product plus it has a run time that if it runs to long it wont run no more and wont until you unplug it and back in to reset it. plus the little pump that comes with it works awsome cant complain.

working great in my 5.5 aio, no problems at all, much better than my jbj ato.

product works great easy hook up run tihs on my 40 breeder with 20 gallon sumop no problem keeping the water level thanks brs

The Nano time-out can be overridden. READ YOUR DOCUMENTATION, as the step-by-step procedure is listed in plain text on pages 27-29 of the manual.

As for securing your waterline properly, a bracket has been included for rimmed and rimless tanks. Again, read your documentation. If the included bracket is not sufficient, then you should think about using an airline mag holder or suction cup. But do ensure you do NOT submerge the tubing below the waterline.

Onto my review:

I own 4 of these units for a variety of tank types, from a picotope 3 gallon to my 46 BF. I have had only one small problem with a snail hitting the float and starting the pump prematurely. Fortunately, the float activates at a level the snail could not reach once filled with water. Aside from needing a little bit better of a pest filter, I love these things. I have the JBJ ATO as well, and it doesn't perform as well. I love the fact that I can buy a switched outlet for the tunze so that I can use my own pump. I have yet to do this, as the included pump is more than sufficient.

I've found this system not only to be one of the best ATO's on the market, but also the most affordable for the benefits! This thing is VERY small as well, the postage stamp sized controller is awesome! I really cant say enough about the quality of this product.

Ive found for the best performance, submerge the entire float assembly below the water line, and gradually raise it till the float switch activates, then raise the mount about 1/16". This will make the float very sensitive to level fluctuations. (FYI my float activates when it reaches just below the halfway mark of the plastic mount)
For those of you installing this in an AIO, you'll find it a much quieter installation if you have the water fill line aimed against one of your inner chambers, or onto the media rack. (No waterfill noise)

I was a little disapointed to find it only uses one float and a snail guard. I'm using in a AIO tank which gives plenty of room to adjust the float/snail guard inside the chamber. It also has no electronic eye or backup float, as well as no warning lights or audible alarms. Does the job, although not as nice as my regular tunze osmolater.

I have always used the JBJ ATO's for my previous reef set ups, i wanted to try something different, and Tunze has always been one of my favorite and more solid brands in the industry. This ATO tops of more constantly to compensate for any evaporation with a nice safety feature of shutting the pump off after 3-5 minutes if for some reason float got stuck or your evaporation was excessive.

this type os ATO is for sump only, as the previous reviewer stated, so if you don't have a rear filtration from an all in one tank or a sump for your tank, it may be very difficult to set up as you do need an area where evaporation is visible for the float to be in and activate once water is low enough.

Overall, this is a great unit, i am pleased with it as well as BRK's fast shipping and deals.

Just installed this last week on my 29G BioCube. This unit is simple, yet very effective. The quality of this ATO is above average. I was deciding between this ATO and the JBJ ATO. I like the fact that this is a complete package with the return pump.

It works flawlessly! I don't really have to worry about snails/critters touching the float valve because it is contained securely in Chamber 3. I also have a fish saver that prevents any animals from getting into the back. I would be concerned if the float valve was in the main display tank, since there is no "backup" float valve.

The magnets are really strong, and easy to adjust your water level. I don't have any concern about the magnets gettting mistakenly moved, they are very strong.

I also like the fact that the ATO has a automatic failsafe built in... turning off after a minute and a half....that turns out to be about 3/4 of a gallon of water. Highly unlikely that you will dump your entire resovoir of water into your tank.

I can hear the pump kick on every now and then. Probably not as accurate as the optical valve...but it works great. It keeps my water level consistent. I am getting better skimmate from my skimmer. I don't have to monitor the tank as much now either. My salinity levels are now more consistent.

I have an SPS dominant systems with large Acro Colonies. My tank has been up for the past 8 years. Everything is thriving. The Osmolator Nano is a really nice unit, not too expensive or overkill. It works perfectly, as advertised.