Scale, algae, and debris are still left clinging to your pond. Left alone it can build up and hurt your pond’s look and ecosystem.
But you have a pressure washer.
Holding it too close to the rocks can damage them, the beneficial bacteria, and the liner, so take care! 8” or more is enough room to clean the rocks with damaging anything.
The pond part of the pond is now clean, but the rest isn’t.
You can learn the importance of rocks and gravel to koi ponds >>