I have approx 140gallons in the pondless waterfall. I built it 10 years ago and it has done fine. It’s about 25’-30’ long. I loose about 60 gallons a day. The check valve is working, so no pipe leaks. I don’t see anything obvious, the water is confined to the spillway. I don’t know if it is possible to loose that much water over that 25’-30’. I don’t remember it loosing that much in the past.