I am guessing a blockage as well. I have had my hob forever and even though my return is close to the bottom of the sump I have never had a syphon break during a power outage. Only problem ever was algae buildup. A black piece of acrylic can end that for ya as well as gutter guard on the "teeth."
Here is what I did to stop it. I turned off the return, CLEANED UP THE FLOOR AND SURROUNDING AREA, the water slowly drained out of the HOB once clear I slowly opened the return and tada it has been working since.
Thanks for all of the responses. I really do appreciate the input.
