I've lived in this house with this pool for 2.5 years, but the house is 30 years old, so I assume the pool is also. Not sure when it was last re-plastered, but it's been a long time for sure (I also doubt it's ever been re-tiled, but that's for another discussion). Anyway, there are some very noticeable stains that I am curious about. About 50% of the top step has a brown stain and there are some areas deeper in the pool that have some gray looking stains. I assume the top step stain has to do with sunlight and poor circulation of water at some point, but that's just my guess as a newb. Can anyone tell from the picture what caused these stains and if there's some method to try to remove them or lighten them? If there's no trick, it's all good. I will just live with until I can afford to replaster it.