I have six running at the time, I do see one varying current threw my apex im sure its not 100% but I cant see it in the flow, Im going to swap it and see if it is the same as another. I have built skimmers and foam fractionators with these pumps ..there great. I will bet money says you can put a 12000 impeller on smaller units and get more flow. they all share the same head, just different motors and impellers. There all interchangeable , Also you can buy needle wheel for them...great pump for the money...