We just had to turn the filter off Whenever it is on the pond leaks!!! Im going to get it sorted today, what could be wrong?

Did you check around the pipes that lead to and from the filter? Maybe a connection is lose, and when the filter is turned on, it rins out from there. The water level doesn't go any lower if the filter is off, right?

sounds like leaking pipe? or if external pump/filter could be leaking pump, or crack in the bottom of the filter?

I hope you find it quick and it's not too extenive to fix/replace.

Scott