Our pool has some brownish stained areas, and many spots and areas around the pool that are rougher (like sandpaper) or marked like the surface was chipped or eaten away by something, where you can see something dark like a black spot underneath. Functionally it isn't causing leaks or cracks, but algae clings to these spots more than other surfaces and makes it hard to clean. We are finishing up our first SLAM and these are the places I am having the most trouble ridding of algae. My pool is old and we have only owned it a year, so I don't know if it has ever been resurfaced. My question is, what are the best options for getting rid of these spots? I know that we could have it resurfaced in plaster/gunite whatever its called. Other than that are there any good options? Any idea what would be most cost effective?