I have just dug a half acre pond. my soil conditions are a sandy clay mixture. I know I need to add a liner but am confused about what to use. I am considering 20 Mil HDPE Poly. Some say it is ok, some say I should use 30 Mil. This will be a fishing pond with no access for wildlife. I will be adding Christmas trees for structure.I need your help guy's, The dam is done and I am ready to put in the stand pipe.