Lucky to find Pete Leong - I love that the videos are not too long well explained and easy to understand so I simply had to provide a shelf for these videos for you to enjoy and come back to at a later time.
I did not expect that an ND4 filter would be used in this shot so the point is to try to get a slow shutter speed to get the blur - of course tripod is a must. But watch the video for the full detail.
I'm going to have fun next time I find myself with a handy fish tank on the side. I would like to see how my camera can handle this.
A filter that is actually graduated is used to cover the sky part and give it that effect is used here.