DANG Leaks!!!

[rig]

Hi,
Hoping to get some help here. I built a smallish pond in my garden, and cannot keep it topped off enough. It is basically an upper pond (800-1000 gals), and a lower catch basin ( maybe 8-10 gals) which feeds into the skimmer.  If I turn the pump (which sits in the skimmer) off, and let things settle, both the main pond as well as the catch basin remain full and at a constant level, which means they are not leaking....right? But when I turn things on, the level in the catch basin falls about an inch an hour until the pump is running dry. The level in the upper pond itself remains constant. I've been at this for about  2 months trying to figure it out...NOTHING. I cannot maintain an adequate water level in the catch basin to keep things going. Perhaps the catch basin is too small???
Anyone have ANY ideas?
Thanks,
Robert

[howardTheHumble]

Robert it could be a few things but I think I have your answer and it is not a leak.

The water level in the 1000g pond increases when the pump is running.  This means you are pumping more water in then you will get back until the 1000g pond reaches it max level.  That is why the level in the catch basin falls over time.

You can add additional water to the system to make it work but when the pump stops it will overflow.