The system I built is from the Endless Food Systems DIY plans. I used untreated pine for all my grow beds, and treated pine for the sump tanks that will sit on the ground, as well as the leg supports. To line the beds, I did a lot of research, and settled on DuraSkrim pond liner. It’s what aquaponics farmers use to get organic certification. I was overly concerned with using plastics and how the leaching could impact the quality of the plants. It’s really hard to get away from plastic, since galvanized metal is poisonous to fish. Unless you have the time to let algae coat all the surfaces, the zinc will be toxic. I emailed a friend of mine in the plastics industry, who happens to have a lot of the same concerns I do, and she recommended I go with the DuraSkrim. I ordered a roll online, but realized later that my local aquaponics store (Brite Ideas in Austin) carries it as well. I could have saved so much on shipping!