Pond losing water

Question:
My water level dropped really fast in my pond.
My pond is abot 800 gallons and this morning.  I woke up to find that there was a 6 inch loss of water.  (BTW it rained really hard that night) and after I came back from school there was about the same amount, so i know it's not a leak. The day before the water level was stable.  I have never had this happen before, so could you kindly tell my why this happened and if it is normal ?

Thank you for your time.

 Answer:
First turn off your pump, then fill the pond. Watch it for 24 hours. Then turn on your pump and see if you can see where the water is leaking off the back.
If you have a fountain, the water can be blowing out if you had a storm. If you have spitters, the water can be drooling out of that. No water leaks that fast, so it's the pump.
Check all connections, but chances are a rock tipped and water is falling off the back or the side.