Do Salt Generators damage limestone/masonary

[chem geek]

That's interesting about the spa. You say it's the same water, but it's elevated in temperature isn't it? That would make it less corrosive and more saturated with calcium carbonate (but then after splash out, I would expect it to cool off and be more corrosive again). What is your Calcium Hardness (CH) level? I saw everything else in your post, but not that (also what is the temperature of your pool and of your spa, typically). Also, if your spa has jets, then I expect that it's pH might be higher than the pool (due to more aeration and therefore more carbon dioxide outgassing) and that also makes the water less corrosive (assuming your pool and spa water aren't thoroughly mixing which I assume they are not since otherwise you couldn't keep elevated spa temperatures for long). Have you ever checked your spa pH separate from your pool pH? Also, have you ever checked your spa's FC separate from your pool FC? Those would be interesting numbers. Though the salt may be a contributing factor, it may be that your pool water chemistry is on the corrosive "edge" to begin with so that salt makes it worse. Perhaps keeping the pool more saturated with calcium carbonate *might* help. Let me know the extra info and we'll see if I'm full of it!

Richard