I really like those stock tanks that hold like 1,000 gallons or more, they are basicly round horse troughs. I have seen people turn those into ponds. My only concern would be about is rusting either above or below ground. How would one protect that metal and expand its lifetime. It crossed my mind that maybe the tank could be Rhino lined inside and out. I dont know if the chemicles used in the Rhino linning would affect fish health or water quality. That stuff lasts longer than any exposed metal. Or would you have to use some kind of paint to protect the metal? Or could you just line the inside of the tank with pond liner, some sand and paint/protect the outside of the tank? Thanks!!!
