+ You can add the HEDP now. It will help prevent further stains, might remove some existing stains, and will keep the metal in the water once the ascorbic acid breaks down (which it will as soon as you begin adding chlorine again).

+ Plain 6% household bleach.

+ Zero chlorine is NOT safe; any chlorine level up to 50 ppm is safe for kids, but above 10 ppm may not be safe for swimwear if your stabilizer level is low.