If there is going to be a legit waterworld later I suggest making the water acidic. Not like burns-you acidic, but enough to affect the life there in some cool ways. I was reading about Europa, and they think it is acidic and it would stop ocean organisms from developing calcium carbonate bones like on earth. Vivianite was a proposed replacement they could have evolved with, which would be cool. Transparent slimes with a visible skeleton or snails with crystal shells. Coral reefs made of crystal!
I also hope we see a hydrothermal vent when we are down there.
I also hope we see a hydrothermal vent when we are down there.