I catch my minnows now. I have tried to keep minnows in the past and I know what you are going through I use to buy mine by the pound. They can be expensive especially if very many die. I have used old deep freezers and the commercial spin type minnow agitators. I have used Better bait and other products also. But the best thing that I have done to keep minnows is to keep them in the lake that I fish. I use a 5 gallon bucket with a top. I cut the bucket half into add a piece of 1/4" hardware cloth in the middle of the two pieces making it how ever tall you want it as to how many minnows you need to keep. I drill holes use the small plastic zip ties to build them. Then I tie mine to a old post that is out in about 8' of water in the lake about 2' below the surface of the water. You could also tie it to a dock also or a old tree out in the water somewhere. When I get to the lake they are already there and they stay healthier than any other way I have tried. I have been doing this for years now and maybe I have been lucky but no one has ever bothered them. I catch my minnows in the family pond with a cast net and use 4 leaf clover traps that I also make myself. You can see how to build these traps on youtube. One other thing I remember is if you use any water with chlorine it will kill your minnows. Well thats how I do it, hope this helps. Good luck with the minnows