You could mean a few different things, so describing the situation more fully would help.
- is the water a green swamp?
- is the water clear but the pool surface is stained?
- does the pool look fine but you want info about automatic cleaners like the Polaris?
Each of these would want very different answers.
I've never done any power washing so take the following as no more than pointers to direct your own further research.
In this thread you were asking about dealing with a rough surface, which probably means an acid wash; I don't know anything specific about how to do that. You can search for posts and probably find some useful information.
If, in addition to that, you have stains from organic matter (algae etc) then a bleach solution is probably best. On the other hand, organic stains are likely to fade on their own if you simply maintain an elevated FC level after you refill, as well.
If you have any reason to suspect metal stains, you want to look into an ascorbic acid treatment.
Hopefully others with more experience in one of these operations will be along to provide more helpful information.