Sometimes its the size of the minnow you are using and depth your float is set at, not that you didn't know that already. Just the other day, I threw on a minnow, little bit over 2", and no takers. Put another minnow on, little smaller, put in same spot, bam, fish on within seconds. I also put a heavy bell sinker on hook, temporarily, and cast in spot I'll be fishing, that tells me how much deeper or not, to set my float. Or they could just be full? Frustrating no doubt though. All that you more than likely already know, but throwing some suggestions out there. Good luck.