Best Pool Metal Remover

Metal is the green pool that shock makes worse

Roughly one green pool in five has no algae in it at all. The walls are clean, the water is clear but tinted, and it turned green within hours of adding chlorine. That is dissolved copper - or, less often, iron or manganese - being oxidized by the chlorine into a colored form. Shocking it again deepens the color. The diagnosis, with the bucket test that settles it in a day, is on green water that is not algae. This page is what to buy once you know.

Where the metal came from decides how often you will be buying: well water carries iron and manganese; a heater core running at low pH sheds copper; a copper-based algaecide adds it directly; and a mineral cartridge is designed to. Fix the source, or you are sequestering forever.

Two products, two jobs

The word remover is on both labels and neither removes anything from the pool. A sequestrant keeps the metal invisible; a lifter moves it from the wall back into the water, where it is invisible only if you then sequester it. That is why the two are used in sequence, and why buying only one of them so often looks like the product failed.

How we compared them

• **A stated dose per volume.** Pool Mate publishes a quart per 10,000 gallons; Doheny's Metal Out publishes 4 to 6 ounces per 10,000. Clorox publishes none on its listing. A dose you can check is a dose you can size and price.
• **A stated active ingredient.** Only Doheny's stain remover states one - 100 percent ascorbic acid. No sequestrant here names its chelating agent or a percentage, so none can be compared on strength, only on stated dose.
• **What surfaces the maker states.** A lifter stated for vinyl and painted surfaces is one you can use on them. One that is silent is not something to assume.
• **Honest limits.** Clorox limits its stain-removal claim to fresh stains. That is correct, and any listing claiming a sequestrant removes an old stain is overclaiming.

Dosing the two that publish a dose

Test for metal before you buy either one

A sequestrant added to a pool with no metal in it does nothing you can see, and an ascorbic acid treatment on a stain that is not metal wastes a day of deliberately low chlorine. A copper and iron test - a strip made for it, or the free water test most pool stores run - tells you in minutes whether the problem is real and which metal it is. Copper points at a heater or an algaecide; iron at well water or a rusting fitting; manganese, which stains purple-black, at well water almost every time.

The order that works for tinted water

1. **Stop adding chlorine for a day.** More oxidizer makes more color, not less.
2. **Sequester at the label dose,** with the pump running so it distributes.
3. **Run the filter continuously for 24 to 48 hours.** Sequestered metal is filterable, and a clarifier helps a sand filter catch it - see clear cloudy water fast.
4. **Bring chlorine back up slowly.** If the tint returns as it rises, the source is still feeding metal into the pool.
5. **Find the source.** Test the fill water, check heater pH, stop any copper algaecide, and consider replacing part of the volume if the fill water is the problem and you have better water to replace it with.

The order that works for a stain on the surface

1. **Lower free chlorine to near zero.** Let it fall, or use a chlorine neutralizer. Ascorbic acid at 3 ppm chlorine is simply wasted.
2. **Lower pH to the bottom of the range.** The lifter works faster in slightly acidic water.
3. **Apply the ascorbic acid,** sprinkled directly onto a floor stain or broadcast for wall staining, pump running. Watch it - a metal stain visibly fades within hours. If it does not move at all, it is not metal.
4. **Sequester immediately, the same day,** at the full label dose. The metal you just lifted is in the water and will re-stain as soon as chlorine comes back.
5. **Bring chlorine back up over two or three days,** testing pH as you go.

The picks

Top pick - A stated dose per volume

Pool Mate Concentrated Metal Out, 1 quart

Publishes its dose per 10,000 gallons on the listing, which most sequestrants do not, and names the eight metals it is for.

The published figure

Sequestrant dosed at 1 quart per 10,000 gallons; listed for calcium, cobalt, copper, iron, lead, manganese, nickel and silver

Pool Mate states one quart treats 10,000 gallons. That is a real, checkable dose - a 20,000 gallon pool needs two quarts, and you can work that out before you buy rather than after.

A sequestrant does not remove metal from the water. It binds it so it stays dissolved instead of dropping onto plaster as a stain, and it degrades, which is why the label says to re-dose through the season and at closing.

The listed metals include copper and manganese, the two behind most green and purple water that is not algae - see green water that is not algae.

What it does well

• Dose per 10,000 gallons stated on the listing
• Names the specific metals it targets
• Recommended by the maker at opening and closing, which is when it matters

What it costs you

• Will not lift a stain that has already set
• No active ingredient or percentage stated
• A single bottle is one treatment, not a season

Skip it if the stain is already on the wall. A sequestrant prevents; it does not remove. Buy an ascorbic acid product for that.

$12.82 - View on Amazon

$14.92 · 14% off

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Pick 2 - Lifting a metal stain that has set

Natural Chemistry Extra Strength Stain Free, 1.75 lb

The product that actually takes a stain off the wall - which is also why you sequester immediately afterward.

The published figure

Industrial-strength ascorbic acid blend, 1.75 lb; stated to remove metal staining from all pool surfaces without adding phosphates

Natural Chemistry states an industrial-strength ascorbic acid blend for metal staining on all pool surfaces. Ascorbic acid - vitamin C - lifts iron and copper stains by reducing the oxidized metal on the surface back to a soluble form. It works within hours and the change is visible.

The catch is where the metal goes: back into the water. Without a sequestrant straight afterward it re-stains within days as chlorine re-oxidizes it, and the maker says as much in recommending its own Metal Free as the second step.

Chlorine has to be near zero for it to work, because chlorine oxidizes ascorbic acid before it reaches the stain. Let chlorine fall first, treat, then bring it back up slowly.

What it does well

• Removes a set metal stain rather than merely preventing one
• Stated for all pool surfaces
• Adds no phosphates, unlike some stain products

What it costs you

• Needs a sequestrant immediately after or the stain returns
• Requires dropping free chlorine to near zero first
• Does nothing for organic staining or scale

Skip it if the water is clear and the walls are clean. This is a rescue product; use a sequestrant for prevention.

$29.08 - View on Amazon

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Pick 3 - Season-long maintenance dosing

Doheny's Metal Out for Swimming Pools, 32 oz

At 4 to 6 ounces per 10,000 gallons a bottle goes five to eight times further than a quart-per-10,000 product, which changes the price comparison completely.

The published figure

Concentrated sequestrant dosed at 4 to 6 oz per 10,000 gallons; 32 oz bottle with a dosage view stripe

Doheny's states 4 to 6 oz per 10,000 gallons. A 32 oz bottle is therefore five to eight doses for a 10,000 gallon pool, against one dose from a Pool Mate quart. Whether the two are equally strong per ounce is not something either label lets you check, so compare cost per dose rather than per bottle.

The dosage view stripe on the bottle saves measuring, which is a small thing you appreciate at the fifth dose of the season.

It is a sequestrant, so the same rule applies: it prevents staining and does not remove a stain that has set.

What it does well

• Low stated dose, so one bottle covers a season of maintenance
• Dose stripe marked on the bottle
• Dose per volume published

What it costs you

• Does not list the metals it targets the way Pool Mate does
• No active ingredient stated
• Will not lift a set stain

Skip it if you need one heavy dose on a badly stained pool at opening. Lift the stain with ascorbic acid first, then use this to hold the metal in solution.

$19.99 - View on Amazon

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Pick 4 - A stated 100% active ingredient

Doheny's Pool Stain Remover, 100% Ascorbic Acid, 2 lb

States its content plainly - 100% ascorbic acid, nothing else - which is the one claim on this page you can check against a chemistry textbook.

The published figure

2 lb of stated 100% ascorbic acid; listed for iron, copper and manganese stains on plaster, vinyl, fiberglass and painted pools

Doheny's states pure ascorbic acid and names iron, copper and manganese plus organic staining. On metals the mechanism is reduction, as with the Natural Chemistry product; on organic stains it is only the acidity, and it is weaker there.

Two pounds is the larger container here, and because the content is stated as 100% active you can dose by weight against the stained area rather than guessing at a blend.

Sprinkle directly onto a floor stain or broadcast for wall staining. Either way: low chlorine first, sequestrant after - the same two rules as every ascorbic product.

What it does well

• 100% ascorbic acid, stated
• Two pounds, enough for a whole-pool treatment
• Stated safe for vinyl and painted surfaces as well as plaster

What it costs you

• Same re-staining risk without a sequestrant afterward
• Chlorine has to come down first
• Weak on scale, which is not what it is for

Skip it if the stain is white or gray. That is calcium scale, and ascorbic acid will not move it.

$31.94 - View on Amazon

$34.49 · 7% off

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Pick 5 - Hard water plus metals

Clorox Pool&Spa Scale, Metal and Stain Control, 1 quart

Covers calcium scale as well as metals, which is the right combination on hard fill water - and it limits its stain-removal claim to fresh stains, which is honest.

The published figure

1 quart; stated to prevent metal stains and scale formation and to remove fresh metal stains

Clorox claims prevention of both metal staining and scale, and removal of fresh iron and copper stains. Fresh is the operative word: a sequestrant can pull a days-old stain back into solution and cannot touch one that has set over a season.

The scale claim is what makes it the pick for hard water. High calcium with high pH deposits scale on tile and in the heater, and the same chemistry that holds metal in solution holds calcium.

No dose per gallon appears on the listing, so the label decides it.

What it does well

• Handles scale and metals in one product
• States the limit of its own stain-removal claim
• Widely stocked, so easy to re-buy mid-season

What it costs you

• No dose per volume on the listing
• Will not remove a stain that has set
• No active ingredient stated

Skip it if your fill water is soft and metal is the only problem. A plain sequestrant with a published dose is more checkable.

$20.98 - View on Amazon

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Well water: treat the hose, not the pool

If your fill water is the source, every top-up brings more metal in and every sequestrant dose is a temporary answer to a permanent supply - which is also why the sequestrant goes in before the shock at pool opening, not after it. The durable fix is a hose-end pre-filter on the fill line, which removes iron and manganese before they ever reach the pool, with a sequestrant handling only what gets past it. Test the fill water directly from the tap; if it reads for metal there, no amount of treating the pool solves the problem.

What none of these do

They do not lower calcium hardness, which is what a white or gray deposit actually is. They do not remove organic staining from leaves and tannin, which brushing and chlorine handle. And they do not stop a heater running at low pH from shedding fresh copper every week - that is pH management, and it is the real fix for the commonest source of copper in a residential pool.

They are also worth dosing at closing, when the pump stops for five months and anything dissolved has every opportunity to settle onto the plaster - see pool closing chemicals.