i am in the process of digging my pond. i planned on a 9x14 pond but it has grown to 9x19. I had ordered a 15x25 goodyear .45 mil liner which should be here soon.. Because I made my pond larger than I had planned I no longer have enough liner left over for the waterfall. I was wondewring if I can use rubber roofing material just for under the waterfall portion or will that affect my fish and plants. I read somewhere that type of rubber was not good for ponds with fish or plants. Or do I have to order the goodyear stuff and wait another week.