Quote Originally Posted by PoolDoc View Post
I very much doubt that the calcium is directly preventing staining.

I suspect that what is happening is that you are creating fine calcium precipitates in the filter, which because of flow and surface area tend to get 'stained' BEFORE the pool does.

If my analysis is correct, this is directly related to the method I've mentioned of using cal hypo to remove metals from the water.
IF that is the case then perhaps this is an easier way to achieve this. I know of others with fiberglass pools who have done this and had similar results. One thing that I did notice is that one time when I let the calcium hardness drop (I fill with softened water) I got stains again. My fill water has no iron (my city water is reverse osmosis where I live and very soft. They add calcium to bring the hardness up some and my house also has a water softener. I suspect the iron was introduces by "pool salt" since the first stains I every saw were in the spot the salt sat to dissolve.)