My 1.5HP Hayward Super Pump went on the Fritz. I just had it replaced with a 1HP Pentair Whisperflo. The sales rep recommended the 1HP size. Anyhow, when I run it on low speed, the pump itself does not fill up entirely with water; it only fills up about 3/4 of the way up to the see through lid. Does anyone know if this is normal? I called the store, but they are closed on Saturdays. I am also wondering if I can change the motor speed while it is running or if I should turn it off first before changing it. The speed control is on a toggle switch.