The slider in the fleece area has 2 sensor: a top sensor and a bottom sensor. The bottom sensor, which has the white wire, is the main sensor. During normal operation, it should be placed about 1/2″ above the water level in the fleece area. As the fleece gets dirty from catching particulates in the water, it will cause the water level in this fleece area to rise. It will rise up and make the bottom main sensor rise up. When the bottom main sensor moves up, it will turn the motor. As the motor turns, it will bring in new fleece. The new fleece will then make the water level go back down which will make the bottom main sensor go back down and turn off the motor. This process is repeated over and over in small increments keeping the water continuously filtered.
The other two sensors with the black wires are shut off sensors. We used two for redundancy. When either of these black wired shut off sensors move to the up position, it will shut off the motor. This is necessary to make sure the motor does not continuously move when the return pump shuts off (for example when doing a water change). One of theses sensors should be placed in the return pump area about 1/2″ above the normal operating water level. If an ATO unit is used that makes the return pump area water level go up and down over time, then you will want to place the sensor about 1/2″ above the highest water level. The other black wired shut off sensor is located on the slider above the bottom main sensor in the fleece area. This is to shut off the motor in case the water level continues to rise in the fleece area. There is also an emergency opening in the fleece area that will allow the water to empty out into the skimmer/refugium section in case it rises preventing the sump from overflowing.