I just watched a You Tube video regarding the use of those large 250-330- Gl plastic containers, The individual wrapped the inner plastic insert with black, 6 Mil plastic to keep out the sunlight thus reducing the groth of algae which is good but normal plastic sheeting that he used will deteriorate in no time due to untra violet rays. If this is the way you want to go just be sure you use UV resistant plastic (and i am not sure it is available in black)