@joRN1414 You can't put 2 pools on top of each other straight and if you raise the pool walls, the floor the pool is in will also have higher wall. Only way I know of to achieve similar to what you want is to cheat. If you know how to make above ground builds with foundation (bridges), the process is the same. If you don't, there's a link thread that has a video guide how to do it.
Using that method, you first build the above ground foundation room in the air and place a pool to it - use windows that have as big of an area of clear glass as possible on the walls (depending on wall height and what packs you have). You basically have a floating fish tank. Now you can build a pool under that and use the vertical arrows on the floating room to lower it very close to the pool under it but can't touch it. Only way to make the floor of the floating room transparent is to use the see through dance floor giving a somewhat illusion of 2-story fish tank... That's the best I can think of.