Evaporation is every tank owner’s constant enemy. Automatic Top-Off (ATO) systems provide convenient assurances. The products use water from a reservoir to refill tank or sump levels. This helps maintain specific gravity and salinity. In particular, this is important in reef and marine tanks. Drops in these levels increase stress on fish and can be fatal. Below are four of the best-selling ATOs available today.
Tunze developed the automatic refill system in 1985. They have over 30 years of experience building ATOs. The Osmolator, short for Osmotic Regulator, is one of the most advanced. In fact, many tank owners consider this the “Gold Standard.” This unit is fresh, reef and saltwater compatible.
The Tunze 3155 ATO is an all-in-one unit. This product includes two sensors. The 3155 ATO comes with the tubing, pump and power supply as well. This is a submersible pump. A high and low-level alarm alerts owners to water drops. If desired, owners can turn off these alarms. LED lights provide visual alerts too. A word of caution: the controller does not hold up to water. It is not remotely water resistant. Do not spill on this unit.
The sensor unit measures roughly 2.5” in diameter. A small, optical sensor provides readings. Infrared technology makes these readings very accurate. A second sensor comes as back up. This is more of the traditional floating style. If both sensors fail, the ATO will shut the pump off after 10 minutes. Once the sensors resume working, it turns the pump back on. Users have noted that power surges auto-start this unit. If your power flickers, the ATO will start auto-filling when power comes on. Similarly, if you unplug it and plug it back in, it starts pumping.
Set up is easy with the compact 3155 ATO. Sensors attach to the tank via magnetic mounts. This ATO’s sensors can attach inside a sump filter as well. The included instructions provide four set up scenarios. Please pay careful attention to the siphon directions. This unit may overflow your tank or reservoir if set up wrong. A sensor placed in the reservoir will turn the pump off once emptied. This safety precaution prevents dry-running the pump.
- checkThe 3155 Osmolator is compact and small.
- checkThis ATO unit is easy to install.
- checkThe infrared sensor provides accurate water readings
- checkA back up sensor provides peace of mind
- checkThe 3155 operates quietly
- The 3155 is expensive when compared to other units
- Cloudy water can trick the infrared sensor
- The controller is not waterproof or water resistant. Do not get this wet
- Beware of back siphoning. Follow instructions
- Power surges cause auto-filling
JBJ is a well-known brand in the world of fish tanks. This JBJ ATO has mixed reviews. Many users love the JBJ brand and this product does not disappoint them. However, users who do have issues report poor customer service. Please remember to register your device on the JBJ website. At JBJ, second hand units are not subject to warranties.
The JBJ ATO Controller does not include all necessary components. Owners will need to buy the pump and hoses separately. (Several users recommend the Cobalt MJ400 pump for use with this product.) The large controller measures 6” wide, 6.5” long and 2” deep. It provides users with LED and audible alerts. Included are directions for silencing these alarms.
The JBJ ATO comes with two sensors. Both of these are traditional float sensors. Built-in guards prevent snails or other organisms from attaching to the floats. JBJ claims the sensors activate the ATO within seconds of a water drop. Please clean these sensors on a regular basis. Floating sensors can fail if organic matter collects on their surfaces.
It is possible to set up the JBJ to refill a tank or sump filter. The electronic control provides two modes for operation. It also permits for three different set up scenarios. This unit comes with a pre-set automatic 3 minute 45 second shut off. This acts as a “Float Fail Safe”. Owners can extend this time to 14 minutes as well. The unit will shut off if the reservoir is low too.
- checkTwo float sensors activate within seconds
- checkRelatively inexpensive for an ATO
- The pump and hoses are not included
- Float sensors are outdated technology
The AutoAqua Smart ATO is the smallest listed in this article. The AutoAqua Smart ATO is best for small or minimalist tanks. This unit does not contain floating parts. For most ATOs, floating or moving parts create the greatest amount of problems.
This ATO is another all-in-one product. The package includes the control, sensors, pump, tubing, and mount. This pump is submersible. Unlike all other items in this article, this includes a siphon valve. Some users note the pump does not provide sufficient power for large tanks. A stronger pump can replace the one that comes with the unit if needed. The controller unit runs large. Expect a 10.2” long by 6.5” wide controller.
The AutoAqua includes a single sensor. As with the Tunze 3155, this sensor is optical. It utilizes AutoAqua’s Quick Security Technology. As a micro sensor, this item is the size of a penny. This makes it convenient to obscure from view if desired. The sensor can attach to clear, tinted or painted surfaces. The magnetic mount is strong enough to connect the sensor to ½” or less planes. To clean the sensor, dip it into vinegar. Be careful not to scrape the lens. This can result in false readings.
Set up with the AutoAqua ATO takes little time. Directions and YouTube videos provide ample clarity. One key point: LEDs can be problematic. AutoAqua advises that owners do not mount this near any bright light. This can cause issues with the infrared water level readings.
- checkExtremely small sensor for convenient placement
- checkThe optical sensor provides accurate water readings
- checkThe pump runs quietly
- check2-Year Warranty
- This is a single sensor unit.
- Bright lights can result in problems
- The pump may not support large tanks
- This product is costly
Innovative Marine sells their ATO as a complete kit or in pieces. The kit will not include hoses. The Hydrofill ATO works for fresh and saltwater fish tanks.
The complete kit comes with a pump, controller and tank bracket. Unlike the others, this includes a diaphragm pump. This means that it runs outside of the water. Heat reduction and dry running provide safety reassurances. The pump has a built-in valve. Thus, it includes back siphoning safeguards. The controller indicates use via color-coded LEDs.
This ATO includes two sensors. These sensors are unique. The two-pronged sensors use low-voltage currents. The currents use the water to relay signals between the prongs. Low water will result a current break. This triggers the ATO pump. The dual sensors allow users to set high and low points. Because they are small, use of the sensors is discreet.
The bracket will mount to rimmed or rimless tanks, as well as sumps. The pump has three placement options. Set up is easy. Innovative Marine touts this item as “out of the box” ready. Strong adhesive tape allows the controller to attach almost anywhere. At 5.12” long, this controller is one of the smallest on this article.
- checkDual sensors allow for custom high/low water levels.
- checkThis ATO includes small, discreet sensors.
- check1-Year Warranty for the pump and controller.
- This does not have an auto-off sensor for a dry reservoir.
- The tubing is not included with purchase.
Automatic Top Off systems provide many benefits. They help tank owners maintain water levels. They also help prevent salinity fluctuations that can cause stress for fish. Built-in safety precautions make different ATOs stand out. Units with optical sensors tend to be more expensive. However, these products are usually more precise. Units with dual sensors provide their own backup system. If one should fail, the other remains in work. Audible alarms and LED indicators help owners know when a pump is on. Auto-off functions can help increase safety. They prevent the pumps from running dry when the reservoir is empty. Back siphoning is an issue with most ATOs. Following the included directions to prevent this is key.