Will this be a flat finish, not a shiny or glossy finish?
It is a standard finish for this particular product. It won’t be flat, nor glossy, it will be some in between.
It’s a salt water pool, how can I maintain concrete surface?
Okay, by mentioning ” to avoid salts” mainly was for driveways, sometimes homeowners dispose a big amount and it eats concrete surfaces. In your case, as long as the salt in the pool is balanced, it shouldn’t have any side effects on concrete. Also I would suggest to wash the deck with fresh water, to avoid accumulation of salt when in use.And last the stain sealer that we going to use has some type of protection, will apply 2 coats.