Auto top off system.

[Douglas]

I have a problem with my auto water top off system and am seeking advice. I'm using a Tsunami AT1 sensor, and a Aqua lifter aw-20 vacuum pump, from a reservior. I tested it to see if the sensor was working, and it is, but the water does not shut off...it's like it creates a siphon and constantly fills the sump. Looking for helpful scientific advice to fix the problem. Thanks, Doug