When I used to keep minnows for my fishing partner who used to think that they helped I used a 110 gallon rubber livestock tank made of recycled tires. I have had it for several years and it doesn't rust and the sunlight does not deteriorate it. As for water circulation I just used a standard Coy pond pump and attached a hose to make the water splash thru the surface. I have kept minnows alive for over a month without feeding them in it. I also used it in the cold months when I did not feel like cleaning fish and had only a dozen or less, it would keep them alive until I decided to clean them. Keeping minnows alive is a little tricky so I would recommend trying it with just a dozen or two to start before you bought them by the pound. It is less painful to loose a dozen minnows than to loose a pound of them.