Waterbear,

I don't see how having DISSOLVED calcium would help; maybe there's some sort of ionic effect that raises the staining threshold. If so maybe Chem_Geek has some info on that. But what I've pretty much confirmed is that if you make the water PASS THROUGH calcium particles, especially in a high oxidizing state (ie, cal hypo via the skimmer) you WILL stain the heck out of the goo on the filter.

Now, if you are precipitating calcium onto the filter, maybe THAT will help.