Why is the ATO filling my sump higher than the sensor?
In most cases if the water level has risen above the sensor after top up it is due to a syphon being created on the hose coming from the freshwater reservoir. Included in the bag with the top up pump is a small inline siphon break, this should be fitted on the top up hose when installing the unit. If this is not fitted water can sometimes continue flowing into the sump from the freshwater reservoir after the pump is turned off by the top up unit.
This should be installed so that the arrow on the siphon break is pointing in the direction that the water flows through the tube and should be positioned so that it sits just above the maximum water filling level in your freshwater reservoir. Please be aware that when the pump activates a small amount of water will be released out of the siphon break so it is important that is sits above the freshwater reservoir.
Optical sensors can also, in some cases, be activated by bright light. When choosing a position for the optical sensor make sure it is in a location where it will not get direct light from a cabinet or sump light. This is especially important in aquariums that have sumps built on to the back as these can sometimes be well lit by the main lighting.
For Nano aquariums water fluctuations in a rear filtration area can be normal and can cause the sensor to be submerged, please click here for more information on this.