Cheryl G, how large is your pond and how much water do you add everyday? Evaporation can cause water levels to fall this but if it a significant amount of water you are adding then I would guess you have a leak. We found areas around the waterfall causing this but it could be anywhere. There are other postings on this site to help you find it.
VERY likely a leak around the waterfall
you may have to take it apart and rebuild the rocks
I agree. See how far down it goes. If it stops at a certain point, you'll know the leak is around that level. I wish I could tell you something further, though! Good luck.
Cheryl G Did you fix the leak?
If you have a leak, as it sounds like you do, that needs immediate attention.
After the leak is fixed. so you do not have to add water to the pond yourself, install an automatic water feeder. When the water level drops from evaporation, this device will fill the pond back up to whatever level you set it at... In short, you personally never have to add water again, the system does it for you!
here is a place that will explain better that of which I speak.