We will have a 3 ton moss rock waterfall with 5' weeping walls on each side and 3 bubblers in the sun shelf. PB is recommending a Hayward Tristar EE pump & motor, 1 ½ horse power. Is 1.5 HP the right size? The price is the same as a 1 hp. Does it need to be 2 speed or will we be able to adjust the flow someplace?