Platinum family metals are impervious and offer the best solution for long term durabilty. Chlorine is found with increasing use in household 'non-abrasive' cleaners and of course in laundry detergents and bleach. It is also used in pool and hot tub water treatment and in high concentrations in tap water. In some communities the chlorine in tap water is at levels normal for swimming pools. Where new construction is common local codes require chlorine level boosting each time a new home is connected to the water main.
Chlorine reacts specifically with the copper and nickel portions of gold jewelry alloys.
Copper and silver are the primary alloys for yellow gold and nickel is the primary alloy for white gold. Chlorine dissolves the copper, or in the case of a white gold mounting for a diamond the nickel, and causes a perfectly good and often new piece of jewelry to break. Try to avoid wearing jewelry in the pool or hot tub. Rings set with stones, especially with prongs, are most subject to damage and hot tub water is five times more damaging due to heat and increased chlorine concentrations. Bromine based hot tub treatments are also damaging although not quite as corrosive as chlorine.