Just now saw your response. Not sure still how much as far as total gallons lost. All I have to go on is the fact that it appears to lose about an inch in 24 hrs, but was more a few weeks back when it was much hotter out. We're having another high temp week, so I'm continuing to monitor. I did order materials to rig up a water top off inside the vault.
Yes, I've checked both falls separately for 24hrs. At this point I believe the excessive water loss is/was due to the very hot days we were having, and splashing. I just wasn't paying enough attention I guess. While carefully inspecting everything over the last week, I've noticed that certain areas of the falls were splashing quite a lot onto the outer rocks, etc. The only way to prevent that would be to back off on the amount of water flowing over, which of course would lessen the dramatic effect. Not sure yet what I'm going to do, but likely I'll just keep paying the high water bill! Lol