We are trying to get our pool build wrapped up and were just recently able to turn on the water feature pump. The pump runs 3 scuppers and 2 bubblers. When the valve is turned to run the scuppers only all is well. However, when the valve is turned to send enough water to the bubblers so they are functioning as well the water flowing from 2 of the 3 scuppers decreases to the point where it flows back along our split faced stone wall which we were told can't handle water flowing on it or the stone will erode away over time. The pool builder said he normally runs bubblers on the main pump but our main pump is a variable speed pump so we didn't think there would be enough flow for the bubblers to work and asked him to plumb them in on the water feature pump. The water feature pump is a Pentair model SF-N1-2A rated at 2 HP. I think the water feature pump is undersized. Does anyone know how to determine what size would be appropriate?