I usually trap my own minnows and keep them in a tank. I like having minnows at my place, because I live out in the hills and depending on the day and lake i'm headed to it may be a 5 mile drive to one bait shop or it may be 30+ to another.
I have a 15-20 gallon tank set up that's constantly ciruclating water. I've got a drain in the bottom with an automatic shut off filling in the top. I'm currently flushing around 20 gallons (well water) through it every day, so the water is always staying fresh. I trapped about 1000 minnows 5 or 6 weeks ago and up until now I've had very little loss. The last 2 days i've lost around 150. I check the tank every day to pick out any death loss. It seems like i run into this every year. I did a google search, but didn't come up with anything. I'm wondering if they are starting to starve. Any advice?