Hi,
We go through a lot of minnows here. I keep mine in an insulated bait bucket downstairs where it's cold. I have a cheap air bubbler with an air stone at the end of the plasitc tubing. I let the air run all the time. Oxygen cold are the top things. I also clean the water at least once a day and take out the dead minnows. I have good luck with this method. I haven't really found anything the minnows seem to eat. I throw in some fish food sometimes but I think they are so stressed they don't eat. Be careful with minnows as sometimes Sticklebacks are mixed in and they have spines that protrude and may hurt the turtles. They have a sharper shaped face and body and when they swim their front fins kind of move in a fanning motion...