As to the maxi jet, it sounds like your system is not a needle wheel impeller. It sounds as though it is an injection type skimmer. If so that means your air mixes behind the pump in the water stream, unlike needlwheels that inject the air before the pump. With a needle wheel the impeller actually chops up the bubbles, hence why makign a screen for it breaks them down even further. I don't see what the practical purpose would be for "tuning" the regular impeller on a MJ if the air mixes AFTER it.