We had our pool replastered in January of 2015. We have kept up the pool chemicals and have been good about brushing. Never had an algae outbreak. We do have very hard water with the calcium hardness rising fast with no real reason (we have been around about that on the forum with no answers as to why except the hard water) so we did a reverse osmosis last summer but it is hovering about 500 now not even a year later. Even with all the time we devote to the pool our plaster has developed some slight yellow staining after only a few years. I can see it probably won't be much longer before it looks as bad as it did before we replastered. Is this inevitable? Can anyone keep their plaster white (or whiteish) and for how long realistically? It is very discouraging. My friend in another state had hers replastered about a year before mine, I visited last weekend and it has some black flecks but still looks overall quite white. She doesn't have hard water issues. So, how long realistically before plaster develops stains even with good care?