I would agree that splashed water from the pool onto nails in a wooden deck will corrode them over time. A salt pool (i.e. SWG, though some people add salt without an SWG) will likely corrode such nails faster. In either case, the use of high-quality galvanized nails should help, but as was pointed out the use of screws is even better.

Did the popping of the boards happen due to corrosion of the nails themselves? That's what I would assume, but if it's due to some sort of breakdown or expansion of the wood itself or possibly loss of friction between the nail and the wood, then it would be useful to know that. Also, did your friend have an SWG or pool with added salt? Just trying to keep some statistics on this one way or the other.

Richard