1. Improper Sensor Placement

When using an ATO inside a sump, the sensor should only be placed in the pump chamber. This is because that is the only place where the water level will change with evaporation. The concept is the same for all-in-one style aquariums, place the ATO sensor in the chamber that houses the return pump.  

If you are using hang-on style equipment and do not have a dedicated pump chamber, consider the XP Aqua Sumpless ATO which is the only auto top off system suited for mounting directly inside the display aquarium.

2. Picking The Wrong Size Reservoir

If your reservoir is too small, you will run out of water too frequently which leads to frequent reservoir refills which is most often a manual process. Running your ATO pump dry in an empty reservoir can cause the pump to burn out.

If your reservoir is too large, you risk allowing excessive freshwater to be accidentally added to your aquarium in the event of an ATO failure that results in an overfill. Your ATO reservoir should be no more than 15-20% of your tank's total water volume. 

  • 5 Gallon Reservoir - aquariums up to 75 gallons
  • 10 Gallon Reservoir - aquariums up to 120 gallons
  • 15 Gallon Reservoir - aquariums up to 200+ gallons

3. Neglecting ATO Sensor & System Maintenance

Salt creep and calcareous deposits can wreak havoc on your ATO sensor which will ultimately lead to a failure. You should be removing and cleaning your ATO sensor on a monthly basis or as often as needed for the sensor to stay clean and in working order.  This applies to all types of ATO sensors including float switches and optical sensors.

4. Improper Pump Placement & Plumbing

Always place your ATO pump at the bottom of the ATO reservoir to reduce the risk of drawing air into the pump.

5. Not Mounting The Water Fill Tube ABOVE The Water Line

If your ATO reservoir is on the ground, the end of the water fill line should be ABOVE the water line in your tank or sump.  If you submerse the end of the fill tube in your tank, you could experience a back siphon where saltwater flows back into your ATO reservoir from the aquarium. 

Conversely, if your ATO reservoir sits higher up on a shelf, you could experience a continuous siphon from the reservoir to your tank, even when the ATO pump is not engaged.  Always use a siphon break valve to reduce the risk of overfilling your aquarium.  

6. Using "Contaminated" Water For ATO

Keep your ATO reservoir clean and free of contamination. This could be saltwater that accidentally got into the ATO reservoir or just poor-quality freshwater used to fill the tank.  Be sure to keep up with your RO/DI filter replacements to keep these harmful contaminates out of your aquarium water. Check your filtered freshwater using a TDS meter before filling the ATO reservoir.  

7. Putting The ATO Sensor In The Display

The only ATO system suitable for installation directly in the display aquarium is the XP Aqua Sumpless ATO.  ATO sensors should always be placed into the pump chamber