Prep first
Before you start
- Start with a sponge and a mild soap-and-water solution.
- Rinse thoroughly so no soap film is left behind.
- Identify the metal first, since bare steel, chrome and aluminum each need different care.
- Dry completely, because moisture left on bare steel starts rust.
Black and green growth on metal is usually algae, and moss can settle into the same damp spots on pipes and hinges. Water is the safest first step on metal, while chlorine, acid, abrasives and soaking all need care. For set-in marks on chrome or wheels, the only approach given is the maker's approved cleaner, so check the finish before you try anything else.
Algae on water pipes usually responds to plain water first, so start there before anything stronger. Moss from a water pipe or algae on car hinges is the same story, and abrasives and acid both need care around the finish. If a stubborn mark won't lift, stick to the maker's approved cleaner and confirm the finish before trying a stainless steel cleaner.
Before you start
What metal, chrome & tools can take
Safe to use1
- Water
Use with care6
- Hot water
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
Avoid1
- Heat, once the stain is out
6 items
What you'll need
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- Sponge and mild soap-and-water solutionThe first wash, which loosens slime and dirt on any metal. (opens Amazon)
- Bristle brushLifts stuck-on growth before anything harsher is needed.
- Wire brush or 000 or 0000 steel woolOnly for bare steel, for stubborn spots. (opens Amazon)
- Clean, dry clothsFor rinsing residue and drying the metal fully.
- Oil, silicone spray or another rust inhibitorProtects dry bare steel from rust. (opens Amazon)
- Acid-free metal cleaner approved for your metal typeOnly if soap and water fail. (opens Amazon)
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6 steps
Step by step
Step 1 of 6
Identify the metal before cleaning
Bare steel, chrome, aluminum and painted metal each need different care, so check which one you have before you pick a product. Pipes are not a separate case here, so treat a pipe as the metal it is made of. If you cannot tell, stick with the soap-and-water wash and hold off on anything stronger.
Careful. Chlorine bleach is not safe on non-stainless steel, aluminum or silver.
Step 2 of 6
Wash with mild soap and water
Work a mild soap-and-water solution over the growth with a sponge, letting it loosen the slime and dirt. This is the routine first step for metal, and it is the option that is always safe to try.
Tip. Work in sections so the wash does not dry on the metal before you reach it.
Step 3 of 6
Rinse the metal thoroughly
Rinse the whole area until no soap film is left, paying extra attention to joints and crevices where growth hides. Leftover soap can leave a dull film on the metal, so do not skip this rinse.
Step 4 of 6
Brush off stubborn growth
If growth is still clinging, go over it with a bristle brush first. On bare steel only, step up to a wire brush or 000 or 0000 steel wool for the stubborn spots.
Careful. Steel wool and abrasive pads scratch chrome, so keep them off chrome parts.
Step 5 of 6
Use an approved cleaner only if needed
If soap and water do not lift the growth, use only an acid-free cleaner approved for that metal type. Follow its instructions and do not leave it on longer than the label says, then rinse the area well.
Step 6 of 6
Dry and protect the metal
Dry the metal completely with a clean cloth, then protect bare steel with oil, silicone spray or another rust inhibitor. Once it is dry, the protective coat keeps the bare steel from rusting again.
Tip. Use a plant-based oil on garden tools, and wax or a chrome preservative on bright metal.
Careful. Do not store the metal wet; leftover moisture causes rust.
If you'd rather buy than mix
Best products for algae on metal, chrome & tools
Look for an acid-free metal or wheel cleaner approved for your metal type, and a rust inhibitor such as oil or silicone spray for bare steel.
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on metal, chrome & tools, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
The metal looks clean when the green or black film is gone and the surface feels smooth when you run a clean cloth over it. Bare steel should look even and dry, with no new orange spots, and chrome should look bright with no haze left from the cleaner.
What changes for yours
Adjust for your metal, chrome & tools
Moss
Moss takes in water through its leaves, so it settles where metal stays damp, such as shaded spots that rarely dry. Use the same wash, rinse and dry steps, but expect it to hold on tighter and give the brushing a careful, patient pass.
Once it is gone, dry the spot completely and keep the damp area in mind, because moss returns wherever water keeps collecting.
Car hinges
Car hinges are usually bare steel or painted metal, so check which one before you scrub. Use the soap-and-water wash first and a bristle brush, and only use a wire brush on bare steel.
After rinsing, dry the hinge thoroughly and put oil or a silicone spray on bare steel so it does not rust again. For the painted body panels around the hinges, the Car Paint & Exterior guide covers the right cleaners.
Heavy or long-standing buildup
Growth that has been on the metal for a long time is harder to lift than a fresh film, and a soap-and-water wash may only soften it. Repeat the wash and rinse before you try anything stronger, since the loosened growth comes off more easily on a second pass.
If the growth has dried on, go over it with a bristle brush first. On bare steel only, a wire brush, coarse steel wool or lump pumice will cut through what is left, so work in short passes and check the surface as you go.
Chrome and aluminum cannot take those abrasives, so for stubborn spots on them, stay with an acid-free cleaner approved for that metal type. If marks still show on bare steel after that, a white vinegar soak overnight is for rust, not algae, and no further method applies to these parts.
Vinegar, baking soda, peroxide and more
Do home remedies work on algae on metal, chrome & tools?
Most home remedies were written for fabric, stone or other surfaces, so many of them do not carry over to metal. The ones that fit are a mild soap in water and a careful rinse, and the rest don't suit metal.
Skip4Avoid3
What makes it worse
Mistakes to avoid
Don't mix bleach with vinegar, ammonia or other cleaners.
Mixing chlorine bleach with ammonia, vinegar or other acids or cleaners can form toxic gas. Rinse each product fully before you switch to another, and never combine them in the same bucket.
Don't scrub aluminum with wire brushes or abrasives.
Wire brushes, abrasive cleaners and polishing compounds are listed as unsafe on aluminum, so keep them to bare steel. Stick to a sponge and mild soap for aluminum parts, and rinse well.
Don't clean hot metal.
Cleaners should not go on hot chrome or metal. Let the surface cool first, then start the wash.
When to call a professional
Call in a professional if you are unsure what the metal is, the growth does not lift after the steps above, or the surface looks damaged. Until then, stop and do not reach for stronger chemicals.
Questions
How do I remove green algae from a water pipe?
Start with a sponge and a mild soap-and-water solution, rinse thoroughly, and dry the pipe completely. Treat the pipe as the metal it is made of, since bare steel, chrome and aluminum each have their own limits on brushes and cleaners.
Can I use bleach on a metal pipe?
No, not on non-stainless steel, aluminum or silver, since chlorine bleach is unsafe for them. If you are unsure what the metal is, leave the bleach out entirely.
Does moss come back on metal after cleaning?
It can, because moss and algae spread by wind-borne spores. Moss settles where surfaces stay damp, so drying the metal well and keeping shaded, wet spots in mind helps slow a return.
What causes the black streaks on metal?
They are usually algae, most often Gloeocapsa magma, a blue-green algae that makes a dark pigmented sheath to shield itself from UV light. It is often mistaken for mold or mildew, but it is a different growth.
Can I pressure-wash algae off metal?
Stick with the gentlest method for metal: the soap-and-water wash with a bristle brush. Stronger force can scratch the finish, so let the wash do most of the work.
Is white vinegar good for algae on metal?
Not for algae. White vinegar is only listed for severe rust on bare steel, so it does not belong in an algae cleaning.
How do I keep metal from rusting after cleaning?
Dry the metal completely with a clean cloth, then coat bare steel with oil, silicone spray or another rust inhibitor. That protection keeps bare steel from rusting again once it is dry.
Algae on other materials
Other stains on metal, chrome & tools
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.