Hi Waterbreak;

Suction leaks do NOT cause you to lose pool water; instead, they allow water in. You can easily have BOTH pressure leaks (water leaks OUT of the pool or pipes) AND suction leaks (air leaks INTO the pipes between the skimmer and main drain, and the PRESSURE side of the pump -- the basket is on the SUCTION side of the pump).

Close to the skimmer, it's possible to have a leak that is BOTH a pressure leak AND a suction leak, or to have multiple leaks, but usually one or the other will predominate.

Shutting off lines is always a good way to isolate the problem area.