I have used a pressure washer BUT BE WARNED the pressure can cut through the liner depending on the washer, the nozzel and how close you are to the liner when spraying. I put a couple of pinhole cuts in my old one this way.
I have also used a push style curling broom which worked really well...but was more work...
You gotta scrub. If you can't get in there and do it by hand, make the equivalent of a large kitchen scrubbie and tie it on the end of a broom handle. Circular motion works better than back and forth. Good exercise
If you have an algae problem, then mainly you have a *nutrient* problem and it'd be a good idea to review your management practices as well, otherwise you'll be back where you started pretty soon.
A certain amount of algae is just part of the lifecycle of a pond and it can help disguise the manmade parts of the poond. That said, you either have too many fish or not enough shade. Since I have a lazy streak when it comes to scrubbing, I would provide more plant cover and focus on plants that are good at sucking those fishy wastes out of the water, like water hyacinths (if they aren't illegal where you are). Personally, plant cover (water lillies) did wonders for my pond.