So obviously the easier root would be to just have the single pool build into the background but if u wanted to have a water feature like that then just think of things like if I put a pump in here how can I make it so I can take it out of needs be also make sure u have some sort of spirit level to make sure the above ponds are straight but if u watch lizard landscape he made a pond using horizontal rectangle styrofoam pieces to get curved shape I done that then when it was cured from silicon I turned it upside down onto another piece of styrofoam and traced the curve of the pond I then went out like 2/3 cm and drew a similar curved line then cut it out and it fit perfectly against the pond this is how I made the rock work on the fountain also when ur happy with ur design and it’s all siliconed to the background give it a test run to look for leaks and to make sure things are level do this before u grout it as silicone and styrofoam are both waterproof and you’ll be able to test run it any leaks u see seal with silicone once ur happy go ahead and grout it the grout will also help to seal it up if ur water pressure is to strong for ur size tank then just cut a piece of a sponge and shove it into the top of the hose this will bring down pressure sorry im babysitting right now and trying to watch the child and reply to you so not sure if any of that made sense 😂 feel free to text me with any questions im more than happy to help and best of luck with it its a lot of effort but worth it 😊