Rough Plaster

My IG Salt Water pool plaster is starting to become rough in spots, stained in others and just isnt showing the brilliance of the 3M Color Quartz like when it was installed 4 years ago.

I was planning on draining at the end of this season, and diamond polishing the plaster to a smooth finish. If anyone has any recommendations contrary to this to achieve a smooth and clean plaster finish I am open to ideas.

Once I have the plaster clean and smooth I would like to seal it to prevent any further degradation. Can anyone recommend a sealer that I can paint on the plaster. I want it to be clear so I can still see the color in the plaster, I don't want a paint or an epoxy finish that will go over the plaster.

TIA