Many people first find out that they have metals in their water when unsightly stains appear. Metal stains most commonly appear shortly after the PH is raised or when you add chlorine. Fiberglass pools are particularly prone to metal stains. Organic stains can sometimes look similar to metal stains, but are usually left by algae or leaves that sit in the pool for a while, and leave a stain behind when cleaned up.
Iron is fairly common in well water but rare in municipal water. If you will be filling you pool from a well, have the water tested for iron. If you have iron consider having iron free water trucked in. Copper is in some algaecides, many “mineral” systems, and ionizers. If the PH in the pool goes much below 7.0 for very long, copper can get into the water from a copper heat exchange coil, commonly found in pool heaters. In addition to staining the pool, copper can turn blonde hair green.
You can remove iron stains with Vitamin C, which is ascorbic acid. If you suspect a stain is caused by iron try the Vitamin C test. Simply place, or hold, a Vitamin C tablet against a stain for 30 seconds. If the stain vanishes, or lightens noticeably, in that area you should do an ascorbic acid treatment.
There is no practical way to remove metals from the water short of replacing the water with new water that doesn’t have any metals in it. If you have metals in the water you will need to use regular doses of a sequestrant to prevent the metals from forming stains. Sequestrants bind to the metals and prevent them from depositing as stains. Sequestrants slowly break down in the pool, so you need to add more regularly to maintain the correct level.
ProTeam’s Metal Magic and Jack’s Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) are some of the top sequestrants. You can also find many other brands with similar products, some of which are noticeably less expensive. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.
In rare cases metals can color the water a variety of colors, typically green or blue or yellow. When this happens the water will still be very clear and transparent. If the water is cloudy or murky it is very unlikely to have anything to do with metals in the water. If the coloring is from metals, lowering the PH slightly and adding sequestrant should remove the color.