I tried turning my pool into a fish aquarium, and my fish keep dying for some reason

[dpad]

anyone know why? Its a pretty big pool, I moved all of the plants and aquarium decorations into the pool. I gradually moved the fish from the tank into the pool, i thought it would work. I just wanted to swim with my fish. My dad said he'll talk to the pool store tomorrow. The last time I called the pool store they hung up on me, maybe they think im a little kid. Thank you for all your answers.