Many users find that black liquid is suddenly coming out of the nozzle when using their spa jacuzzi tub. This is not only confusing but can also cause concern about whether the spa jacuzzi tub is damaged, whether there are hygiene issues, or even whether it poses a health risk.
In fact, the appearance of black liquid in the nozzle is not uncommon; it is the result of a combination of substances accumulating inside the spa jacuzzi tub system over a long period.
To solve this problem, it is necessary to explain it from multiple perspectives, including the composition, source, formation mechanism, working principle of related structures, and correct handling methods of the black liquid in the nozzle.
This article will provide a detailed and clearly structured analysis to help you thoroughly understand the causes of black contamination in the nozzle and learn how to prevent it, keeping your spa jacuzzi tub clean, safe, and efficient.
What exactly is the black liquid in the nozzle?
From a professional perspective, "black liquid" is not always a pure liquid; it often consists of a mixture of:
• Mold and biofilm debris
• Grease and human residue flaking from the pipe walls
• Particles from aging and detaching rubber or seals inside the bathtub
• Corrosion products from metal parts
• A mixture of heater deposits and limescale
• Residual bath product residue from incomplete cleaning
These substances accumulate in the circulation system, and when the spa jacuzzi tub is turned on, the water pressure flushes them out of the nozzles, making them appear as "black liquid."
Black sludge is more likely a complex problem than a single source, so understanding its composition is the first step in solving the problem.
Why does black liquid appear in the spa jacuzzi tub nozzles?
The fundamental reason for black substances flowing from the spa jacuzzi tub nozzles is that:
The internal circulation system of the spa jacuzzi tub is constantly in a humid, warm environment rich in organic residues, a natural breeding ground for biofilm, mold, and impurities.
Here are the specific causes:
1. Biofilm buildup leading to black discharge
Biofilm is the most common and most difficult source of contamination to remove from a spa jacuzzi tub.
Its formation process includes:
• Human skin oils
• Sweat
• Cosmetics
• Lotions
• Shampoo residue
• Bath additives
After entering the circulation system, these adhere to the inner walls of the pipes, forming a viscous film.
When the biofilm ages or is washed away by high-pressure water, some debris is discharged from the nozzle as a black or dark brown "mud-like" substance.
Why does it look black?
The organic matter in the biofilm combines with bacteria and mold, forming a dark, adhesive layer.
The longer it stays in the spa jacuzzi tub, the darker the color becomes.
2. Mold growth inside the spa jacuzzi tub pipes
The inside of a spa jacuzzi tub is humid, enclosed, and warm, creating an ideal environment for mold growth.
Mold typically appears as:
• Black
• Dark green
• Brown
This mold adheres to pipes, the back of nozzles, and internal cavities. It is flushed into the nozzles with water flow, appearing as a black liquid.
3. Long-term accumulation of human waste forms a black sludge-like substance
Each use of a spa jacuzzi tub produces the following residues:
• Sebum
• Dead skin cells
• Sweat
• Makeup residue
• Skin lotion
• Sunscreen ingredients
Once these enter the system, they combine with limescale and biofilm to form a darker-colored sludge.
People who frequently use bath oils, milk-based bath products, or essential oils are more prone to developing black sludge.
4. Black Particles Caused by Aging and Detachment of Rubber Gaskets and Seals
The following components in a spa jacuzzi tub are made of rubber:
• Nozzle seals
• Pump body gaskets
• Diaphragms
• Pipeline interface seals
When a spa jacuzzi tub is used for many years or with strong corrosive cleaning agents, the rubber may exhibit the following:
• Embrittlement
• Powdering
• Fracture
These fragments, when mixed with water, become fine black particles that flow out of the nozzle, appearing as a black liquid.
5. Black Oxide Formation Due to Corrosion of Metal Components
Some spa jacuzzi tubs contain:
• Metal bolts
• Internal metal parts of the nozzle
• Metal surfaces of the heater
• Metal septa at pipe interfaces
When these components corrode due to poor water quality or improper use of disinfectants, dark metal oxides are formed.
The appearance includes:
• Black particles
• Grayish-black sediment
• Detached metallic paint
These appear as black contaminants as they are flushed into the nozzle with water.
6. Scale mixed with dirt causes "black sludge"
Scale is usually white, but when combined with the following substances:
• Grease
• Chemical cleaning agent residue
• Rust particles
• Biofilm
• Mold spores
It turns into a dark gray or black paste.
These substances are flushed into the nozzle as the spa jacuzzi tub is running, resulting in black wastewater.
Why does a spa jacuzzi tub produce black sludge more easily than a regular bathtub?
Black sludge appears much more frequently in a spa jacuzzi tub than in a regular bathtub because its structure makes it easier for dirt and grime to accumulate.
The reasons are as follows:
1. Spa jacuzzi tubs have a closed circulation system
Unlike regular bathtubs, water in a spa jacuzzi tub enters:
• the pump
• the pipes
• the nozzles
• the inner cavity
• the air mixer
These areas cannot be cleaned as easily as the surface of a bathtub.
2. Warm water environments promote biofilm growth
Most spa jacuzzi tubs use:
• water temperatures of 35–40°C.
This causes bacteria and mold to multiply at an accelerated rate.
3. High-pressure water flow causes a "stripping effect."
When the pump is turned on, the pressure flushes out deposits inside the pipes, removing black sludge.
4. Incomplete drying over a long period leads to microbial growth
After use, a large amount of water remains inside the pipes of a spa jacuzzi tub, and even when drained, it cannot be completely emptied; this phenomenon is called "stagnant water."
Stagnant water promotes the long-term accumulation of mold, bacteria, and biofilm.
Will the black liquid sprayed from a spa jacuzzi tub damage the equipment?
The answer depends on the source.
Harmful conditions include:
• Rubber gasket powdering → can cause leaks
• Metal corrosion → can damage nozzles and heaters
• Pipe biofilm → can clog nozzles and increase pump load
• Mold growth → can affect pump efficiency in the long run
Therefore, the spraying of black sludge is often a sign that the internal system of the spa jacuzzi tub is "aging" or "needs deep cleaning."
How to thoroughly clean the black sludge from the spa jacuzzi tub nozzles?
To fundamentally solve the problem, a complete system cleaning is needed, not just wiping the surface of the spa jacuzzi tub.
The following are effective steps:
1. Use a spa jacuzzi tub-specific pipe cleaner
It can:
• Break down biofilm
• Remove grease
• Remove mold
• Remove deposits inside the pipes
Ordinary cleaners cannot work on the biofilm inside the pipes, so their use is not recommended.
2. Circulate the cleaning agent in hot water for at least 15–30 minutes
Use hot water to help break down residue, then use the pump to flush out internal contaminants from the system.
3. Clean and scrub around the nozzle
A large amount of biofilm debris can accumulate inside the nozzle.
4. Second flush (without cleaning agent)
Ensure all residue is removed.
5. Clean or replace the filter
Filters are often clogged with black contaminants and require:
• Deep cleaning
• Or replacement with a new filter cartridge
6. Check rubber gaskets and nozzle seals for aging
If black particles appear rubbery, replace the relevant parts immediately.
How to prevent black liquid from reappearing in the spa jacuzzi tub nozzles in the future?
Preventive measures include:
✔ Use a pipe cleaner regularly (at least once a month)
Keep the internal channels free of biofilm buildup.
✔ Shower before use
Reduce skin oils and skincare products from entering the spa jacuzzi tub.
✔ Use oil-free bath products.
Avoid oily bath products that can cause buildup.
✔ Drain and dry after each use.
Minimize stagnant water.
✔ Replace the filter regularly.
Keep the circulation clean.
✔ Use recommended disinfectants.
Avoid using overly strong or incompatible chemicals that could damage rubber parts.
Why should international buyers choose LOVIA SPA as their long-term manufacturer?
International buyers prefer LOVIA SPA because we deliver a combination of trust, quality, and value. Our factory has 35+ years of experience, certified products, fast delivery, and flexible customization. We provide responsive sales support, accurate quotes, and global logistics assistance. Our reputation as a top Chinese spa brand ensures you buy from a manufacturer that values quality as much as affordability.
