Pictures would be helpful. When you say six inches, how many gallons would you estimate that is? How much water does the basin hold?
Losing water in a pondless while the pump is on vs off is a bit different from a pond. You've eliminated splashing and evaporation by turning off the flow of water and all the water gets stored underground where it is less likely to evaporate. It does eliminate the possibility that the basin in leaking though so that's good.
My pondless waterfall has required more than the usual number of fill ups this season - no rain and lots of windy days contributes to that. Normally I'll fill it in the spring and not have to touch it with a hose again for weeks. I've had to refill it four or five times already this year. But I also know my other water features are all experiencing the same amount of water loss so it doesn't concern me.
When you say "the bucket where the pump is" what exactly to you mean? Is the pump in the basin or somewhere else?
Pictures would be helpful as well, so we can pinpoint some areas of concern.
