denoising adds seconds. It is definitely worth looking in to. It works with DOF too, so you might be able to play with that.
Also you can do DOF in post in a better way. Render out a depth map of your scene. You can put that in one of the channels slots and use Lens Blur in photoshop, choosing that mask. It will look much more realistic. Right now it just looks like you’ve got vaseline on your lens or something. Something that used to be done for portraits, but not so much anymore.
Regarding the water. Well, if those are real plants, perhaps the water is just too clear then. Most people I see that have that kind of setup, the plan is no longer living. Or is just straight up fake. So more common is sand, marbles, dirt and moss, or rocks. But like I said, I was looking for things that seemed to either give it away as a render, or seemed out of place.