Auto Top off System: a look at the Most Reliable Water Level Controllers

Just about every aquarium and reef tank owner know that leveling the tank water is simply one of those things you have to do. What else can you do? It’s the nature of water that they evaporate, and it is part of your job to replenish the water that you’ve lost.

But just in case no one’s ever told you, there’s actually such a thing as an automatic self-leveling controller for your fish tank.

My pick is the Tunze, keep reading for more options!

What is an Auto Top Off System?

Factors to Consider when Buying

Top rated Aquarium ATO

With these factors in mind, let’s take a look at some like candidates for your tank:


1. JBJ Automatic Top Off Water Level Controller

With this ATO, you get the basic setup of the controller, the two float sensors, and two brackets.

You’ll have to get your own reservoir, pump, and tubing. The JBJ receptacle can handle pumps up to 2amps.

It comes with several additional features, besides the automatic refilling and leveling off. It has an Audible Alert, and it also has a “Float Fail-Safe”.

This failsafe turns off the power to the pump after 3 minutes and 45 seconds of refilling, so that you won’t overfill the tank in case the sensors fail. You’ll then need to restart the controller by resetting the float sensors.


    • It works simply when all you want to do is to replace the evaporated water when you’re gone for a long vacation. When the water level reaches the low sensor, it will fill up. When the water then reaches the top sensor, it’ll stop.
    • It can work really well, especially when you also get your tubing and pump from JBJ. There’s no better compatibility than products made by a single manufacturer.


  • That float failsafe may be too short of a time period, and unfortunately there’s no easy way to change this. Theoretically, you can set it for up to 14 minutes, and it involves opening the box to turn a dial. Don’t they have engineers who can give us a dial on the outside?
  • The audible alert can also be turned off. Again, you have to open the box.
  • There are too many reports of breakdowns and failures when you read the reviews online. If you’re lucky, you can get one that works like a charm, but if not you end with broken sensors.

2. Autoaqua Smart Automatic Top Off System

Now this isn’t just an automatic top off system. It’s a smart ATO. It includes the pump and the tubing, which can pump at 74 gph to a height of 6.5 feet. It has a universal holder too.

In addition, it uses a unique contactless digital sensor. It also has built in AFS (Auto Feedback Security) technology for real time failsafe protection.


  • Since it already comes with a pump, all you really need is a bucket for your reservoir water.
  • The sensor contains no moving parts and there’s absolutely no chance of leaking voltage.
  • It gives an alert if it doesn’t fill up, or if the fill up time takes too long.
  • It also comes with a 2-year warranty.


  • You’ll find the same problem with the Autoaqua Smart—it’s not all that reliable. It may work for a while, and then it may not.
  • And then in about a year or 18 months, you may have some rust issues.

3. Tunze Osmolator Universal 3155

This is the gold standard, although it’s also the priciest. It’s the price that may tempt you to look elsewhere, but Tunze has been making automatic self-leveling controller units since 1983.

This also uses a safety float sensor, but only as a backup. Instead, it mainly uses an optic mini sensor. It also includes a pump as well.


  • This very rarely fails—if ever. It really is that good.
  • The installation is very easy.
  • It’s reasonably quiet.


  • It’s expensive. However, if your tank is less than 55 gallons, there’s a version for that size and it has a nice price.

Final recommendations

There’s no question about it—get the Tunze Osmolator. You really get what you pay for, and you can really depend on it. In the end, that reliability is the most crucial factor of them all.

If you think there’s something better out there, chime in and gives us your ATO recommendations!