Finding a mysterious black, sticky substance in your pool skimmer can be unsettling, especially if you’ve taken care to maintain crystal-clear water. This slimy or tar-like material raises concerns about the cleanliness of your pool and whether it might indicate a more serious issue. In this in-depth article, we’ll explore the possible causes of this substance, why it appears, how to eliminate it, and most importantly—how to prevent it from coming back. Whether you’re a first-time pool owner or someone with years of experience, this guide will walk you through the science, solutions, and smart maintenance practices to keep your pool in top condition.
Understanding the Mystery: What Exactly Is the Black Sticky Stuff in the Skimmer?
Before jumping to conclusions, it’s important to assess the nature of the black substance. It might not always be the same thing from pool to pool. Here are the most common culprits:
1. Organic Debris Buildup
The most common explanation is a buildup of organic matter such as algae, leaves, grass clippings, dirt, and other debris that gets trapped in the skimmer basket. Over time, these materials can decompose and turn into a sticky, dark substance.
2. Slime from Algae and Biofilm Growth
Algae, especially black algae, can grow in pools if the chemical balance is off or if the filtration system isn’t running efficiently. Algae not only discolors the sides and bottom of the pool but may also accumulate in hard-to-reach places like the skimmer, forming a black, slimy buildup.
Biofilms, which are communities of microorganisms that adhere to surfaces, can form in the skimmer if there’s a consistent nutrient source and inadequate circulation. These films often appear slick, dark, and may emit a faint odor.
3. Contaminants from Pool Accessories or Equipment
Sometimes, the black substance comes from the breakdown of materials like rubber seals, plastic components, or even from pool toys or cleaning tools that have started to degrade under sunlight and pool chemicals. These materials can leave behind a dark, gummy residue, especially when exposed to water over long periods.
Why It Matters: The Risks of Ignoring Skimmer Buildup
While it may seem like a minor annoyance, the presence of black sticky material in the skimmer could lead to more significant issues if ignored.
1. Decreased Efficiency of the Pool Filtration System
The skimmer is one of the first points of contact for debris removal in your filtration system. When it becomes clogged or gummed up with black residue, water flow is restricted. This affects the overall efficiency of your pool system, leading to cloudy water, increased chemical demand, and poor circulation.
2. Potential Water Chemistry Imbalances
Trapped debris can release organic compounds into the water, disrupting the carefully balanced chemical levels. This includes lowering chlorine levels and increasing the demand for sanitizers, which can open the door to algae outbreaks and cloudy water.
3. Risk of Bacterial or Algae Infestation
If the black substance is due to biofilms or algae, allowing it to persist can introduce bacterial elements into your pool. This poses potential health risks, especially for those with sensitive skin or respiratory conditions.
Diagnosing the Problem: How to Identify the Source
Rather than speculate, take a methodical approach to identifying what’s causing the sticky substance in your skimmer.
Step 1: Visual Inspection of the Substance
- Texture: Is it slimy, rubbery, or sticky like tar?
- Smell: Does it have a musty, earthy, or no smell at all?
- Location: Is it only in the skimmer or also visible along the pool walls or return jets?
Step 2: Test Your Pool Water
Proper water chemistry is critical in determining the root of most issues. Check the following:
| Parameter | Recommended Level |
|---|---|
| pH | 7.2 – 7.8 |
| Chlorine | 1 – 3 ppm |
| Alkalinity | 80 – 120 ppm |
| Calcium Hardness | 200 – 400 ppm |
High alkalinity or low chlorine can contribute to algae and bacterial growth.
Step 3: Look at the Equipment
Check pool toys, cleaning tools, and the seals of return fittings. Are there signs of deterioration, discoloration, or residue transfer? It could be that the equipment itself is melting or shedding in contact with the pool water or skimmer.
Clearing the Problem: Steps to Remove the Black Residue
Once you’ve determined the source, the next step is to clean the skimmer thoroughly and ensure that the problem doesn’t spread throughout the pool.
1. Manually Remove the Visible Debris
Begin by emptying the skimmer basket and scrubbing the inside walls of the skimmer using a soft brush or sponge. Use gloves and a long-handled tool to reach down into the throat of the skimmer if necessary.
2. Use a Pool Skimmer Cleaner or Hydrogen Peroxide Solution
Commercial skimmer basket cleaners can break down oils, scum, and organic matter trapped inside skimmers. Alternatively, a diluted hydrogen peroxide (3%) solution can be effective for non-chemical alternatives. Soak the basket or spray the solution into the skimmer chamber.
3. Shock the Pool and Brush the Surfaces
If the residue is due to algae or biofilms, shock treatment with a high dose of chlorine is necessary to kill off microorganisms. Also, brush the pool walls, floor, and any visible crevices where algae might hide.
4. Run the Filter Continuously for 24–48 Hours
After cleaning the skimmer and treating the water, run the filter system non-stop. This allows the circulation to draw up any remaining contaminants and helps restore water clarity.
Stopping the Issue Before It Starts: Preventive Measures
Prevention is always better than cure when it comes to pool maintenance. Here’s how to keep your skimmer clean and avoid future surprises:
1. Regular Skimmer Maintenance
Clean the skimmer basket weekly during peak season and bi-weekly during cooler months. Rinse off stuck-on debris and inspect for signs of wear or bacterial growth.
2. Ensure Proper Water Chemistry
Maintaining balanced pool chemistry is one of the most effective ways to prevent organic matter buildup and algae contamination. Use a digital tester or test kit regularly, and adjust levels before they drift too far from the ideal range.
3. Use Enzyme-Based Pool Cleaners
Enzyme treatments are designed to break down oils, lotions, and other organic materials that can’t be filtered out easily. Add them weekly to reduce scum lines and prevent sticky buildup.
4. Inspect and Replace Pool Accessories
Degraded pool toys, O-rings, and seals can be the silent culprits behind unexplained residue. Replace any rubber or plastic components that show signs of cracking or color change.
5. Minimize Organic Load in the Pool
If the pool is near a garden, trees, or grass, natural flora can contribute to the buildup in the skimmer. Installing a cover or using a windbreak may help reduce the intake of leaves or pollen.
A Note on Weekly Maintenance Routine
Consider this quick routine to keep your skimmer in tip-top shape:
- Empty and rinse skimmer basket
- Brush off any residue inside the skimmer housing
- Test and adjust water chemistry
- Inspect filter and pump operation
Advanced Solutions: When the Problem Persists
Sometimes, the black sticky stuff recurs despite your best efforts. Here’s what to consider when dealing with recurring issues:
Deep Clean the Skimmer and Return Lines
If you suspect biofilm in the lines leading to and from the skimmer, a deep cleaning with non-acidic line-cleaning chemical may be necessary. These products are designed to remove biofilm without damaging the plumbing.
Check for Leaks or Water Infiltration
Black residue that appears suddenly and seems wet even after cleaning could signal an underground leak or groundwater infiltration. This is uncommon but can introduce organic-rich soil materials into the pool.
Call in a Professional Pool Technician
Persistent contamination or recurring black gunky matter in the skimmer may indicate a larger issue—such as a defective seal, faulty equipment, or even an undersized filtration system. A qualified pool technician can perform a full inspection and recommend long-term fixes.
Conclusion: Proactive Pool Skimmer Care Pays Off
The black sticky stuff in your pool skimmer may appear alarming, but it’s typically a sign of preventable buildup rather than a catastrophic issue. By identifying the source and taking proactive steps—such as regular cleaning, water balancing, and replacing worn pool equipment—you can ensure a cleaner, safer pool for years to come.
Remember, understanding the root cause and maintaining a weekly maintenance schedule is the key to keeping your skimmer—and your pool—free from unsightly residue. Whether it’s a few strands of decaying algae or residue from pool gear, solving the problem starts with awareness, prevention, and consistent care.
So the next time you peer into your skimmer and spot that dark film, don’t panic. With the right tools and knowledge, you’ve got everything you need to restore your pool to prime condition. Safe swimming!
What is the black sticky stuff in my pool skimmer?
The black sticky substance that often accumulates in a pool skimmer can be a combination of several contaminants. Common culprits include mold, algae buildup, residues from pool chemicals, and organic materials like oils or dirt. Mold can thrive in damp, dark environments and may appear when the skimmer basket is not cleaned frequently enough. Additionally, algae can form sticky biofilms that adhere to the skimmer walls and basket, especially in pools with poor circulation or inadequate sanitization.
Another possible source is residues from sunscreen, lotions, or other organic matter brought into the pool by swimmers. These can chemically react with chlorine or other sanitizers, forming stubborn deposits in the skimmer. In some cases, petroleum-based products from cleaning materials or pool equipment may leach into the water and stick to the skimmer components. Identifying the exact source can help determine the most effective method of removal and prevention.
Is black sticky residue in the skimmer dangerous for my pool or health?
While the black sticky residue found in your pool skimmer is generally not harmful to your health, it can be an indicator of underlying maintenance issues. The presence of mold or algae can compromise water quality and sanitation, especially if left unchecked. Poor circulation or improper chemical balance may lead to larger issues such as algae blooms or bacterial growth, which could pose health risks to swimmers if the pool is not properly treated. It’s important to assess whether the residue is biological or chemical in nature.
Furthermore, persistent buildup can clog the skimmer basket and impede water flow, potentially leading to equipment inefficiency or damage. Though not immediately dangerous, ignoring the residue can contribute to long-term maintenance problems. Regular cleaning and inspection of the skimmer and pool water chemistry are essential for preventing such issues from escalating and ensuring a safe and enjoyable swimming environment.
How can I remove the black sticky substance from my pool skimmer?
To safely and effectively remove the black sticky residue from your skimmer, start by removing the skimmer basket and brushing off any loose debris. Soak the basket and the skimmer interior in a solution of water and pool-safe cleaner or diluted bleach (1 part bleach to 10 parts water). This helps break down biological growth like mold or algae. Use a soft scrub brush to gently remove the residue without damaging the plastic surfaces of the skimmer.
After scrubbing, rinse thoroughly with clean water and inspect for any remaining buildup. If the residue persists, a mild solution of vinegar and water can dissolve oils or chemical deposits. For tougher stains or sticky films, consider using a commercial skimmer cleaner or a small amount of baking soda paste. Always ensure all cleaning agents are rinsed completely before resuming normal pool operation.
How often should I clean my pool skimmer to prevent buildup?
To prevent black sticky buildup in your pool skimmer, it’s recommended to clean the skimmer basket at least once a week. More frequent cleaning may be necessary during periods of high pool usage, heavy pollen seasons, or after storms when more debris enters the pool. Keeping the skimmer basket free of organic matter and oils will help prevent mold and algae growth, maintaining optimal pool filtration and circulation.
In addition to weekly cleaning, a thorough skimmer inspection and deep cleaning should be done once a month. This includes checking the skimmer walls and throat for any residues or clogs that may not be immediately visible. By maintaining a consistent cleaning schedule, you can minimize the chance of stubborn buildup and keep your skimmer functioning efficiently.
Can pool chemicals cause black residue in the skimmer?
Yes, certain pool chemicals, especially if not properly dissolved or stored, can form a black sticky residue in the skimmer. Trichlor tablets, which are commonly used in skimmer feeders, can leave behind a dark, sludge-like substance if they dissolve too slowly or if water flow is insufficient. Chemical imbalances can also lead to reactions between chlorine stabilizers and oils or pollutants in the water, resulting in dark deposits.
To prevent this type of buildup, it’s important to use a floating feeder or a dedicated chemical feeder outside the skimmer whenever possible. If you must use the skimmer to dispense chemicals, ensure that water flow is adequate to fully dissolve the tablets. Regular visual inspections and skimmer cleaning can help catch chemical residue before it accumulates into a more serious blockage.
What can I do to prevent the black sticky substance from coming back?
Preventing a recurrence of black sticky substances in your skimmer starts with maintaining balanced pool water and practicing regular cleaning. Ensure your pool’s pH, chlorine, and alkalinity levels are consistently within recommended ranges. This inhibits algae growth and prevents chemical reactions that lead to residue. Also, consider using enzyme-based pool treatments, which help break down oils and organic materials before they settle in the skimmer.
Another effective preventive step is to install a skimmer sock or mesh bag filled with activated carbon or enzyme media. These accessories trap oils and other impurities before they stick to the skimmer walls. Reducing reliance on trichlor tablets by switching to alternative sanitization methods, such as a saltwater system or liquid chlorine, can also help eliminate chemical-based buildup. By combining proper chemistry with physical filtration and regular maintenance, you can keep your skimmer clean and efficient.
Should I call a professional if I can’t clean the skimmer completely?
If you’ve tried various cleaning methods and notice that the black sticky residue continues to form rapidly or seems to be coming from within the skimmer plumbing, it may be time to consult a professional pool technician. Persistent buildup could indicate a more serious issue such as biofilm development inside the pipes, algae infiltration into hard-to-reach areas, or chemical feeder malfunctions. These problems may require specialized equipment or treatments to fully address.
Professionals can perform deep cleaning services, conduct water tests, and inspect your pool’s circulation system for hidden clogs or inefficiencies. They can also recommend better chemical management strategies or skimmer modifications to prevent future issues. Calling an expert is especially worthwhile if the residue is accompanied by cloudy water, musty odors, or poor filtration performance, as these symptoms suggest that your skimmer might not be functioning as intended.