How would you design a planet for an aquatic civilisation?

Hey guys. Let's pretend we're a superior being who populates a galaxy with all sorts of life, and we just made an aquatic intelligent species. What would be the perfect planet like for them? The planet's ecosystem should be based on them, and they should be the apex species. <br><br>For the sake of the argument, let's pretend we made a humanoid species made of a flesh similar to that of an octopus, so they would thrive in the ocean. They have suckers on their arms and are capable of changing color similarly to octopi. They can also breathe outside of the water, but would rather not. <br><br>The aquatic humanoid creatures, which we'll call the Ztil, should have a habitable space to match the surface of earth, so they have just as much space as us to build an empire, except they would need to live in the ocean. <br><br>Also, assume this is an earth-like planet elsewhere in the universe, so you don't have to worry about comets or asteroids or anything like that. <br><br>What would you change, or what characteristics would you give the planet in order to make it perfect for our aquatic friends?