We installed an IG pool last year with a SWG and I love it! We've had a problem with chronic rusting on the screws on the returns, light, and skimmer boxes, and also very light rusting on the ladder and handrail. I've been careful to maintain the pH, FC, salt, Ca, and other levels within the guidelines in this forum. Iron levels in our water are not high at all. I had been running the filter 10-12 hours per day and we're about to open for the 2009 season.
The builder did put on an anode at construction time which they claim prevents this, but obviously something else is wrong. They have replaced the screws twice now and will probably do so several more times just this year unless it is fixed.
What could be causing this? I suspect a grounding/bonding issue, though everything checks out according to the builder. What else can be done?