Had this same model essentially for 8 years now and finally replacing it. Worked great and this one was setup and doing its job in minutes. Good stuff.

So far so good. Solid built, quality components. Compact with less wires than my previous set up. Easy to set up.

Super easy to set up and get going. Literal plug in and go. Only thing to note is there is no siphon break so be careful with your tubing placement/pump level.

Seems like I get a year out of the optical sensor. Bought one in January 2024. Had to replace it in February 2025. Just noticed it went out again. Didn’t get a year out of the second one. Will be looking at other brands. This will be my third ATO since my system has been running. Pump is quiet. Really is a hands free system. But the durability is junk at best.

Only been running this for about a week but I really like it. Much more compact and easier to deal with than previous models. Setup was really easy. I don't miss float valves at all!

Using with 10 gallon reservoir in a newish 180 gallon setup. So much easier than manually topping off. Sensor works just as expected on multiple tests.

I like this new model because it has less cords to deal with. It's pretty quiet and doing what is suppose to do.

Been running one for almost a year now and it’s been perfect. Started on a 25g and now on a 100g. Got the nano version for the 25g since the regular Osmolator is oversized for a 25g. Pump is silent and the new sensor/controller combo is so much better than the old design.

I have always wanted the previous generation Osmolator on other tanks, but never pulled the trigger. This one is great, my only niggles, the pump is NOT silent, but it's not loud either. The other niggle is that I do not care for the tube holder, I would prefer something that aimed the tube directly down and you had a couple of 90 degree turns on it to keep the siphoning to a minimum. Other than that so far it has been flawless.

I bought this to replace my old Osmolator. After chatting with Customer Service, I was told the pump would fit in a standard 5 gallon jug. Unfortunately, this is not the case. The new design will not fit inside a 5 gallon jug like the previous design. While the sensor design might be an upgrade, the great thing about the previous design was simply being able to drop the pump inside a jug.

been working perfect since day one pump is quiet and sensor has a very strong magnet

Bought one of these to keep a small tank topped off while on vacation and it failed on. Plummeted the salinity to 8 ppt, which nuked the tank, it caused the tank to overflow and caused water damage. Very disappointing considering how well the previous ones worked.

Have the Tunze Osmolator 3 on a new build 90 gallon tank. It seemed to work for the first couple of months. Very quiet and no need to prime the pump when it runs out of water. Since then, the sensor does not seem to be working correctly as the pump keeps running until my ato runs out of water, overfilling my sump (but not overflowing.) I have tried cleaning the clear side of the sump and the optical sensor. Its a new build so not much to clean, no algae for example. So far, cleaning and unplugging has not resolved the issue. I recently ordered another unit for a 40 gallon I am replacing, so I am hoping I can find the source of the problem. I have been using Tunze ATOs for several years on a couple tanks and before this, they have been very reliable.

I love this new Tunze ATO. It is truly almost silent compared to the old model's pump. There's no controller on this one, making the setup the easiest of any ATO I've used from Tunze. On the ATO sensor itself, it has a little LED light inside that is green when the water is at the correct level and other colors when it's low or too high. I really prefer these LED lights instead of the old version's controller box with water level indicators & literal beeping sounds. The price of these gadgets always stings, but I have no regrets buying this! I went through 2 Tunze nano ATOs in 2 years on my QT frag tank, and this new model has a 5-year warranty, which gives me some peace of mind!

Awesome definitely worth the money

I never leave a review of anything but since I saw a couple negative reviews I thought I should share my experience. I am sorry to see a couple people have had trouble. My experience has been perfect. The new Tunze Osmolstor 3 has been flawless for me over the last 6 weeks. I travel a lot and must have 100% reliability in my ATO, which is why I chose Tunze. I watched it closely for the first 2 weeks, testing it and challenging the level sensor to make sure it worked every time. I had zero issues. I was gone for a month and came back to no problems. I’m convinced the system is well designed and built. It has an optical sensor and backup thermal sensor built units small package. The top off pump is excellent too. Very quiet. I am totally satisfied.

No more display, no audible alarm, no mechanical high water float switch. It’s all built into an optical sensor that malfunctions after a couple of weeks from an invisible slime. Wipe it with a paper towel and get another few days before it malfunctions again. The new pump is awesome, that’s about it. Should have gotten the old unit.

I originally had the previous ATO from Tunze and this is way better in my opinion. 1) no secondary controller box needed 2) head pressure and height is phenomenal 3) ease of setup Additionally, I love that this ATO can be in normal mode or a higher speed mode which is what I use for a large gallon system.