Although the salt-water in the pool is not corrosive at levels of 3000-3500 ppm, when that water hits the coping and evaporates, it leaves pure salt behind. The pure salt is corrosive and is probably the cause of the corroding coping. At least, that's my $0.02.

In order to isolate the problem, you could try adding the same level of salt to a pool with the same coping and no chlorine generator. This way, if the coping corrodes, you know it is the salt doing it and not the generator itself.

Brad
www.waterworkspools.com