Actually, if it's cavitating then increasing the discharge head (plugging a hole or reducing the hole size) would make it better not worse. If you're really using the booster pump and not the main pump it may indeed be cavitating because they are designed for more pressure at lower flow.Noggin said:Edit: I'm now fairly glad I didn't drill smaller holes. I noticed that my booster pump makes more noise now than it did before and if I plug one of the holes with my finger I get popping sounds at the aerator, which I think may be air inside the unit. Is my booster pump cavitating and does putting more backpressure on it by covering the holes make it worse