I have been looking at books on in ground swimming pools and on their construction along with that I have even looked at the possible idea of buying a house with a in ground concrete pool. The things I have pictured from the books is that some of these swimming pools and large fish tanks are built almost the same way and expect one of them has viewing windows and a more stronger frame to hold in the viewing windows. What I would like to do one day to a old swimming pool is dig out the side of it and build a indoor room along the side of it and make the pool indoors and build viewing windows along the side of the old swimming pool by knocking down one of it's old walls. That way I could turn the old swimming pool into a giant fish tank and convert the pump and drain system to help with the movement of water in the giant fish tank.