gonjah wrote, on Thu, 29 May 2014 20:47:29 -0500:

What is the hardness level of your well water? I've been told hard-water
causes mottling. The cracking? I'm not sure, but it could be related. I
think the only thing you can do is refinish and don't use hard water.
(got $5 to $10 grand to spare?)

Here is a shot of the pool store analysis of the well water this week:
https://c1.staticflickr.com/3/2921/1...a42f6d2f_b.jpg

It says 200ppm for Calcium, which is pretty good for a pool, I think.