There isn't anything such as "gill ich", Cryptocaryon prefers to subsist on a fish's skin, but will invade the gills in severe infections. Typically, people misdiagnose Amyloodinium (velvet) as "gill ich" due to the propensity of that disease to infect the gills first and cause rapid breathing. The spots of velvet can be surprisingly large, causing people to think it is ich.
As was mentioned, the larger white spots are pretty common on new pyramids, I never worry about them. What I do worry about are Neobenedenia flukes. This species almost always has these. Given that your LFS ran a sub-therapeutic copper level, I would also doubt their "deworming" as Neo is very difficult to control. If you see cloudy eyes on this fish, or tattered fins for no reason, consider giving it a 5 minute diagnostic FW dip to look for Neo. That will show up at the bottom of the dip container like tiny gray scale looking things.
Sorry - I can't tell you why the first one died....
Jay