I currently have a Sunterra 1250GPH pump. I bought a pre-form 18″ waterfall. The current pump does not produce enough volume for the waterfall to flow completely across the 18″ of the waterfall. Instead it only drips. Could you recommend a pump that will last when it is on continuously, energy efficient and produce enough water so that the water volume is sufficient making the waterfall complete across the whole 18″ of the waterfall. I currently have 3/4″ inside diameter lines to the pump, filter and waterfall. Thank you for your attention on this matter.
The rule of thumb is 100 gph per inch of weir width. So you will need at least 1800 gph to cover the weir.
Magnetic drives are best for longevity and this Waterfall pump (with multi year warranty) will do a fine job for you:
You might want to go to 1″ or 1 1/4 inch tubing to reduce velocity and increase volume.