Aquarium Auto Top Off (ATO)

Nature Dimensions N-Fill Smart ATO automatically replaces water lost to evaporation, helping keep the water level steady in freshwater and reef aquariums. Shop the N-Fill system and its sensor arm extension and sensor extension cable below.

For installation and everyday use, read the N-Fill setup guide. Our ATO siphon and overfill guide covers reservoir and tubing placement.

Choose an aquarium auto top off system

An aquarium ATO replaces water lost to evaporation. Before choosing one, check where the sensors will sit, whether the holder fits the rim, how high the pump must lift water, and how the refill tube will be secured.

Check the mounting and pump layout

  • N-Fill supports freshwater and saltwater aquariums.
  • Check the holder against your rim profile; the specified maximum glass thickness is 15 mm.
  • The standard sensor arm reaches up to 10 cm / 4 inches below the rim. An optional extension increases total reach to approximately 25 cm / 10 inches.
  • Maximum pump head is 160 cm / 63 inches. Check the vertical lift and tubing route in your installation.

Check the N-Fill installation guide

Understand the safety layers

N-Fill has two float switches monitoring the same water line. Either can request a refill. They provide low-water redundancy; they are not a separate high-water cutoff.

The controller stops a long pump run after about 90 seconds and raises an alarm. Correct outlet and siphon-breaker placement are still required, because stopping the pump cannot stop an established gravity siphon.

Read the siphon and overfill setup checks

What comes with N-Fill?

The system includes the controller, dual float sensors and holder, DC pump, tubing, siphon breaker, N-Neon ATO Tubing Organizer, and US power adapter. You provide a suitable freshwater reservoir. See the current N-Fill product specifications for the complete list.

Do I need the sensor accessories?

Choose the sensor arm extension when the standard arm cannot reach the intended water level. The sensor extension cable adds 5 ft / 150 cm between the sensor and controller. Keep the split connector above the highest possible water level.

Can I use it with a rimmed tank or an AIO?

Check the exact mounting area, rim profile, and water-level position. Glass thickness alone does not confirm fit over a wide plastic rim. In an AIO, the sensor belongs in the chamber where evaporation changes the water level. If the fit is unclear, send us the tank model and mounting measurements.

Read the aquarium ATO buying guide · Troubleshoot an existing ATO setup