Prep first
Before you start
- Act now; the longer green growth sits, the harder it is to lift.
- Lift loose slime with a dull knife, then blot with a dry white cloth.
- Dampen a white cloth with warm water and blot, without soaking the carpet.
Algae that has grown into outdoor carpet leaves a green or dark mark, and the damp backing is what keeps it returning. Carpet backing is the weak point here, since harsh products can delaminate it, so every step has to stay light. Fresh slime lifts with blotting, while a spot that has dried may need several rounds or a professional.
Dab a little mild carpet spot cleaner onto a white cotton cloth and work at the green gently. Moss on outdoor carpet and spirulina on pontoon carpet both fade slowly, so expect a few rounds rather than one. Don't scrub hard, since that pushes the green deeper into the pile.
Before you start
What carpet & rugs can take
Use with care6
- Water
- Hot water
- Oxygen bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Heat, once the stain is out
Avoid3
- Soaking
- Chlorine bleach
- Scrubbing and abrasives
8 items
What you'll need
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- Clean white clothsColored cloths can transfer dye onto the carpet. (opens Amazon)
- White paper towelsThey blot without leaving color behind. (opens Amazon)
- Dull knife or rounded spoonLifts semi-solid slime without rubbing the pile.
- Clear liquid hand dishwashing detergentThe only detergent in the method, mixed mild. (opens Amazon)
- White vinegarFor the second-stage treatment on stubborn spots. (opens Amazon)
- Mist sprayerRinses the carpet without soaking it. (opens Amazon)
- Heavy colorfast objectHolds the towels down over the spot while it dries.
- 3% hydrogen peroxideOnly for stains that remain after cleaning, as a set-in treatment.
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7 steps
Step by step
Step 1 of 7
Blot up the wet slime
Lift any loose, semi-solid slime with a rounded spoon or dull knife first. Then press the wet green with a dry white cloth, working from the edges toward the center so it doesn't spread.
Tip. Switch to a clean section of cloth every few presses so the green doesn't transfer back onto the carpet.
Step 2 of 7
Try warm water first
Dampen a clean, white cloth with warm water and wring it until it is wet but not dripping. Blot the spot and check the cloth to see how much green is coming off.
Step 3 of 7A few minutes
Test and apply the mild detergent
Mix 1/4 teaspoon clear liquid hand dishwashing detergent into 1 cup lukewarm water, and pretest it on a hidden area first. If the carpet is fine, apply it to a white cloth, work gently in from the edges, let it sit a few minutes, then blot. Keep going as long as green transfers to the cloth.
Careful. Never mix the detergent stronger than 1/4 teaspoon per cup of water.
Step 4 of 7
Rinse out every trace of detergent
Rinse several times with lukewarm or cold water from a mist sprayer, blotting after each rinse. Keep the carpet only damp, and go on until no detergent is left in the pile.
Tip. After the last rinse, press a dry white towel on the spot; if it picks up suds, rinse again.
Careful. Detergent left in the pile makes carpet resoil faster.
Step 5 of 7
Add the white vinegar if needed
If the spot still shows after the rinse, pretest 1 cup white vinegar to 2 cups water on a hidden area. Apply it to the spot, blot, then rinse and blot again so no vinegar is left behind.
Careful. Vinegar is an acid, so it is only for spots the lighter steps didn't clear.
Step 6 of 7
Weigh the spot down to dry
Cover the spot with layers of white towels and hold them down with a heavy object. Change the towels as they soak through, and keep going until the carpet is completely dry.
Careful. Anything set on the towels must be colorfast.
Step 7 of 7
Check for wicking as it dries
If the spot comes back as it dries, that's wicking, so repeat the whole procedure and focus on blotting out all moisture. If it still won't come out after that, consult a professional carpet cleaner.
Tip. Check the carpet by touch before you walk on it or lay the towels back down.
If you'd rather buy than mix
Best products for algae on carpet & rugs
Choose a plain clear liquid hand dishwashing detergent with no added color or scent. Leave laundry and automatic dishwasher products on the shelf.
Zep Advanced Oxy Carpet & Upholstery Stain Remover
BISSELL Little Green Portable Carpet & Upholstery Cleaner
Rug Doctor Mighty Pro X3 Carpet Cleaner
Utopia Kitchen White Flour Sack Towels
Empty Spray Bottles 16oz/4Pack
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on carpet & rugs, 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
Each blot should pull some green onto the white cloth, and the spot should look lighter after every round. If it reappears as it dries, that's wicking, so blot out more moisture. If the cloth stays white but a faint mark remains once dry, the growth has set.
What changes for yours
Adjust for your carpet & rugs
Moss on outdoor carpet
Moss holds water in its leaves, so lift the dry, matted clumps with a dull knife or rounded spoon before any liquid touches them. Wetting it first only smears the green deeper into the pile.
Then treat the spot with the same blot, detergent, rinse and vinegar steps, and dry it fast with towels, since moss grows where surfaces stay damp. If it keeps coming back, give that patch more sun and airflow so it dries between rains.
Algae on pontoon carpet and spirulina
Spirulina is a blue-green algae, so its pigment can stay in the fibers after the green is gone. Pontoon carpet gets the same method as any outdoor carpet, but keep the rinses thorough because the color lingers.
If color still shows after the vinegar step, the 3% hydrogen peroxide set-in treatment is the next option, tested on a hidden spot first. Repeat the steps in order rather than jumping ahead, and let the carpet dry fully between rounds.
Heavy or long-standing buildup
A green stain that has been left for days is harder to lift, and it may have worked deeper into the pile. Start by repeating the mild detergent and rinse steps with fresh cloths, blotting from the edges inward.
Once the carpet is dry and the spot still shows, the set-in option is 3% hydrogen peroxide on the tufts for one hour. Use only the drugstore peroxide, pretest a hidden spot first, and blot it up after the hour. Repeat if the color is still there.
If the color still hangs on after repeated rounds, the spot may be past what a home treatment can reach. Large or excessive stains can need hot water extraction, which is a professional job, so that is the next call to make.
Vinegar, baking soda, peroxide and more
Do home remedies work on algae on carpet & rugs?
Most remedies from the kitchen and cleaning cupboard don't belong on carpet, so only a few make it into the steps. Each one gets a straight answer for carpet: works, skip or avoid, with the reason.
Works2Skip4
What makes it worse
Mistakes to avoid
Don't wait for the slime to dry
Green growth that dries into the pile is harder to lift, and the longer a spill sits, the harder it is to remove. Act as soon as you spot it, even if it's only a damp patch.
Don't wipe from the middle outward
Starting in the center and wiping outward drags the green into clean carpet. Work from the edges toward the center, and switch to a fresh section of cloth as it fills.
Don't start with the peroxide
The drugstore peroxide is a set-in treatment for stains left after cleaning, not a first step. Save it until the detergent and vinegar steps have been tried.
Don't pour solvent straight onto the carpet
Solvent poured onto the carpet can dissolve the carpet materials and damage the backing. Dampen a white cloth with it instead and work in gently from the edges.
Don't stop rinsing too soon
Detergent left in the pile makes carpet resoil faster, so keep misting the spot with lukewarm or cold water and blotting after each pass. Stop only when nothing soapy comes up on the towel.
Don't lift the towels too early
A damp backing wicks the stain back up as it dries, so the towels need to stay on until the carpet is completely dry. Replace them as they soak through, and keep the weight on top.
When to call a professional
Call a carpet cleaner if a pretest changes the carpet's color, if the moisture went deep enough that the carpet has to be dried from both sides, or if the spot is large enough to need hot water extraction. When you call, mention the algae, the spot's approximate age, and any product already used on it.
Questions
Is green slime on carpet really mold?
Usually it's algae, which is often mistaken for mold or mildew. Algae and moss spread through wind-borne spores and grow where surfaces stay damp, so the steps here are the right approach.
Is white vinegar safe to use on carpet?
Yes, but only as a later step. Diluted white vinegar, 1 cup to 2 cups water, is a standard carpet spotting solution, and since it is an acid, pretest it on a hidden area first.
Can I use hydrogen peroxide on carpet?
Yes, but only the mild drugstore peroxide, and only for a stain that is still there after cleaning. Put it on the tufts for one hour, blot it up, and repeat if needed. Don't use the stronger strength sold for bleaching hair.
How long should I keep towels on the spot?
Keep them down until the carpet is completely dry, changing the towels whenever they soak through. There is no set time, so check the carpet by touch rather than guessing.
Why does algae keep coming back on the same patch?
Algae and moss spread by wind-borne spores, and they return wherever the surface stays damp. More sun and airflow on that patch help it dry between rains, which slows the regrowth.
Can I use a steam cleaner on algae in carpet?
Skip the steam machine for this one, since heat sets many stains in place. If the algae has soaked deep, a professional can run extraction, which is the one time heat belongs on this carpet.
Is laundry detergent a safe option on carpet?
No, it's a poor choice for this carpet. Laundry and automatic dishwasher detergents can contain bleaching agents that break down dye and some fibers, so use a clear hand dishwashing detergent diluted with lukewarm water, at a weak strength.
How should I dry the carpet after rinsing?
Lay several layers of white towels over the spot and weight them with a heavy colorfast object. Swap in dry towels as they absorb moisture, and keep going until the carpet is dry all the way through.
Algae on other materials
Other stains on carpet & rugs
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.