The latest piece of hardware I was surprised with was the Tunze Osmolator 3 Nano (3151.000). I have used various types of auto top offs in the past utilizing mechanical float valves, gravity siphon, vacuum pressure switches, magnetic float switches, and optical sensors.  Most of these solutions work when they work, but the main issue has been how reliable are they before needing maintenance.  This usually comes down to whether or not the design includes redundancy and fail safes for all the various failures that can happen.

The original Tunze Osmolator product line has always been a benchmark auto top off in my opinion. Why, you ask? The Osmolator water level sensor included an optical sensor for detecting low water level and an emergency float cut-off switch to prevent overfilling. I like the fact that two different switch types are used since they cover a wider range  of failure modes. Redundancy is always a good design practice, but sometimes, using the same technology as a secondary is still susceptible to the same failure modes.  In addition to what technology is used, how it is applied in the design makes a difference.

The most common failures for auto top offs are the following:

• inconsistent water level detection
• false detection of water levels – dirty sensors or stray infrared light, jammed mechanical switches
• possible hardware issues
  • Mechanical Floats valves can leak / get water logged or get stuck and not seal properly
  • Vacuum switch systems can leak and cause inconsistent pressure readings
  • Magnetic Float switches can get jammed with organics, or magnets weaken over time
  • Optical sensors can be contaminated with dirt, and leaky casings can cause false readings and hardware failure

Osmolator 3 Nano

This is the smaller of the two in this family of products. As the name suggests, the 3151 is designed for a Nano tank with maximum head height spec for the pump at 9.84 ft. The sensor only has a single optical sensor with a safety timer to prevent over filling. The 3154 is the big brother. The sensor unit includes a secondary safety optical sensor, the magnet can be used on thicker glass and the pump has a higher head height specification.

From an initial review it is a solid product. I recommend positioning the sensor out of light, even with the cover on, to avoid any film contamination. Time will tell with respect to robustness and longevity of the system like all hardware in this hobby grade segment. Keeping it cleaned regularly should be simple and will keep everything running well.

Pros:

• Compact, heavy duty 12VDC pump with decent head height and super quiet
• Shielded optical sensor to prevent stray Infrared light from false triggers
• Dark shaded hose to prevent light driven biofilm from developing inside the tubing.
• Led Status Indicator for Pump ON/OFF
• Easy pump disassembly for maintenance cleaning

Cons:

• The operability method for changing the safety timer setting
• Led Status Indicator only visible from the side if cover is on