Yes changing spin plate height should help. Is it a 200 lb feeder by chance? I think the extra weight also makes the nesccisty for larger opening above spin plate.
Ok here is Sue's response to sizing your system MB. "Hi Greg ~
I've looked on a couple of aerial sites and his pond is too new. There are no satellite images available. I would need to know size, shape and depth to make a recommendation, but I can't do a design or calculation sheet with out a map..."
Do you wish to draw and fax a picutre and provide depth info? If so we can get you some more info just have to guess on tubing length a bit.
