I been reading this website for over 2 years. Now i will start convert my swimming pool to koi pond. I need all expert suggestion. The pool shallow is 3.5 and deep is 8.5. the pool long 28 and wide is 12. I want the pond is 2 feet above the ground. what should i do. do i need filled at the deep of the pool to equal with 3.5 then build the wall and drop in liner or just build the wall without fill the pool.