ROFL...sorry...but a SeaClone 150 is no where near enough for a 125gallon tank, despite what the manufacturer claims.
Unfortunately I have a 40gallon tank, so I can't recommend a good skimmer for your size...but you'd be better off upgrading than trying to add a second small skimmer. Since you have a sump, look for in-sump models which tend to be more effective due to their design.