I would think that the only way a HOB
skimmer would overflow the tank is if the tank water level was kept too high. When I had a HOB
fuge with skimmer on my 29 gal
tank, I shut the skimmer (which then fed the fuge) off and then added water until I reached a comfortable level. Then I fired the skimmer up and the tank water level dropped. I marked this new level as my 'max running' water level with a grease pencil on a back corner. I then made my manual top off to that level.
Overflows are a cause of poor planning.