I'm glad someone else on this forum has a idea like I have. What I have been doing lately is looking for houses with old abandoned swimming pools on them. If I happen to get a house with a abandoned swimming pool on it in need of major repairs. I plan on tearing out one of the walls. And having a new cement wall built into the side of it that would have several large acrylic viewing windows in it. I would built the fish tank swimming pool hybrid into a natural swimming pool were the pool would have a natural filter system in it to keep it clean. The logic behind me wanting to turn a old swimming pool into a giant fish tank is that that my pet fish who I love a great deal would get to use it 100% of the time. While me the human would most likely only use it 5% of the time.