As a long time frustrated pool owner I've stumbled onto your site and I've learned more in the last few weeks than I have in years prior, so thanks for the great info! One question I had is regarding calcium hardness. My initial test reading was 100 but I see that between 250-350 is recommended for a plaster pool. I went to a local pool store and purchased some "Hardness Plus" to add. The store employee recommended that I bump it up to the lower range, around 200, because the calcium does not go away over time and as I add water to the pool due to evaporation, that additional water(which includes calcium) will increase the CH level in the pool. So, I bought a smaller amount than I had planned to, added it to the pool and I'm now at 200. Does additional water that I add to the pool really contain that much calcium, or is the amount so small that I could bump it up now to 300 and not have to worry about it for a long time?