White cyrstals at seal of heat exchanger?

[bwindrope]

Here goes: So I'm doing some routine cleaning and checking of things on Aeolus and I notice that at the end of my heat exchanger there is a noticeable build up of white crystals. This is at the end where there is a rubber gasket and the end cap is removable. The white crystals are right around the rubber gasket between the exchanger and the end cap. I had just replaced my zinc and pulled it out again to make sure it was fine and it was. Maybe 10% gone. No other signs of corrosion.

What would cause these white crystals to form? I assume they are some salt, but since the exchanger doesn't leak, how would the water get out to form them? For that matter, I get these same crystals on my PSS shaft seal on the stationary side. What's happening? I get that it is some precipitate somehow, but can't figure out how or why.

Basically, what is it, why is it there? Any help is appreciated.

Thanks!