I gave this 4 out of 5 when in reality it should be 4.5 stars. I'll explain that in a bit.

There is a lot to like about his ATO. The redundancy fail safes is a huge one for me. This is used on my 55 Gallon Mixed Reef. Since I am gone at work for 12 hours of the day plus sleep at night I wanted something I could feel secure with. So far this does. This offers more than what you can see on the surface. There are actual adjustments inside the display module. BRS has a good video on this and how to set up. I haven't messed with it however. Everything seems to be solid and it works perfect. I really like the water tube holder as opposed to the one my Micro ATO by SmartATO. It's quiet, only time i hear it is when I hear water trickling in and only for a few seconds. I use a 5 gallon reservoir bucket, no kalk with RO/DI water. I like the over all functionality of this.

The issue I had/have and why I give it 4 (4.5) stars is dialing it in. my tank has a rim on it like most traditional ones do however even getting the water level right at the sensor (not sure where that trigger is on it still) has been difficult. I've already done a water change and even getting the water level right for the sensor, it still wants to spit fresh water in. Not a super big deal but if the water level is set right it shouldn't be doing this. But once it is "set" it does its job flawless. I didn't have this issue with the micro ATO that I am running on a smaller tank.

Over worth the price tag.

Great ATO and I'd recommend it to anyone. The optical sensor works great and the backup float switch is a nice redundancy. The only reason I didn't give it 5 stars is because if your water container is filled higher than the water level in your sump it will back siphon and drain all the water into your sump untill the container level is the same as your sump level. An easy fix is to keep the container lower than your sump if you can but mines on the floor so it's not an option. Now I just fill the container up to my sump water level and it works fine. Some guys run the feed line up to their overflow box to eliminate the back siphon but when I did that it ended up sucking water from my overflow into my ato container and flooded it. It would work if you made sure the line was above the water level in the overflow box but I don't want to risk it. I just have to fill my container more often but I'd rather do that then flood my container or drain all the container contents into my sump. Hope this helps.

I thought this was a great product from the reviews but after I set it up it just started to fill up on its own pass the first sensor, thank God for the back up sensor that shut the pump off. As far as costomer support you can only email them if you live in the USA. I'm still waiting on a reply from them. If you want to here the loud alarm from it over filling a few times a day and them have to drain the water out the sump your self(It will kill your salinity with all the RO water filling up your sump). Stay away, this is to much money to buy a worth less product.
Just an update,I was able to find a number for tunze USA and some things were explained to me that I didn't know. The product has been working well for two days now with no problems.

After about 5-6 years of trusty service my controller finally pooped out. Having used this product for many years I can honestly say it is a very percise product and works great. The set up is not diffucult but does require a bit of thought. In the years that I ve used the Tunze there are a couple things I would recommend people watch out for.
1) the sensor can get a bit crusty over time and when this happens the top off will not work as it should. If you notice some crud on the sensor, take it out and submerge it in white vinegar for a couple hours and then whipe it clean. it should be good to go after that.
2) the pump will not last as long as the controller. If you keep you controller for many years you can expect to replace the pupm a couple times. Good news is that they sell the pump seperatly so you dont have to buy a whole new set up
3) finally the pump is a bit sensitive. If it gets an air bubble in it it will not work. This can happen when the container you are pumping from runs dry. If your container runs dry, refill it and then while submerged tilt the pump upside down (the intake will be facing up). you should see an air bubble pop out and when that happens you are good to go.

I have 4 reef tanks and each has this ATO. The oldest setup is over 10 years old and I have had zero issues. Highly recommended.