Hi, I'm moving on to my 2nd system - a step closer to my aim of a commercial system in the uk. I want to try and heat the water so I am able to grow tiliapia here in our cold climate. What I'm going to try is to use 15'' black guttering pipes as the gb so that the sun heats the water as it flows through. I'm going to insulate my tank so that it acts like a heat store. I hope to keep the water warm enough for the 9 months I need to grow my fish. All inside a polytunnel. Any thoughts anyone ?