Algae in a wooden, saltwater, hydrolysis, or biological pool: complete guide

Algae in a wooden, salt, hydrolysis pool or natural swimming pool? The right treatment depends on your installation. This guide explains the key differences and mistakes to avoid, especially when there are fish or biological filtration.

Warning: never pour chlorine shock treatment into a fish pond or natural swimming pool. If in doubt, do not add any product.

Access the interactive algae diagnostic tool (link to be checked before publication).

Chlorine pool

Free chlorine provides residual disinfection when its concentration and the pH are appropriate. Measure free chlorine, pH, and stabilizer, then check the filtration. Green water may indicate insufficient disinfectant, poor circulation, or organic deposits. Never pour concentrated chlorine onto wood or the liner.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

Salt pool

Salt electrolysis generally produces chlorine. Check the cell, salinity, alarms, and filtration duration. Measure the free chlorine in the water: the displayed production percentage is not sufficient. Clean surfaces gently and check areas with little circulation. Corrective treatment depends on the analyses and the instructions.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Hydrolysis and electro-oxidation

The term hydrolysis refers to several technologies. Some produce oxidizers, while others combine electrolysis, UV, ionization, and regulation. Identify the brand and model before any treatment. A system advertised as requiring no chlorine addition may produce chlorinated species. Do not perform a chlorine shock treatment without the manufacturer's approval.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Bromine pool

Bromine is a disinfectant used in some spas and swimming pools. Its testing and operating conditions differ from those of chlorine. Check the available bromine, pH, and filtration. Do not mix treatments at random. Bromine is not suitable for a fish pond or a natural swimming pool.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

Active oxygen and peroxide

The expression active oxygen can refer to different formulations, including peroxide- or monopersulfate-based products. They do not all provide the same residual disinfection. Read the label and use the appropriate tests. Do not mix oxidizers. A product with a reassuring name can damage biological filtration or harm aquatic animals.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

UV-C

A UV-C device acts primarily on the water passing through its chamber. It does not directly eliminate algae attached to the walls. Check the lamp, sleeve, flow rate, and prefiltration. In a conventional pool, UV-C does not automatically replace residual disinfectant. In a natural swimming pool, follow the original design.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

Ozone

Ozone is a powerful oxidizer used in specialized equipment. Its production, contact with water, and off-gassing must be controlled. Exposure to gaseous ozone is dangerous. An ozonator does not mechanically remove biofilms and does not necessarily guarantee residual disinfection. Consult the manufacturer before making any modifications.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Copper-silver ionization

Mineral systems may use copper or silver ions in addition to other treatments. They require concentration monitoring. Copper can stain surfaces and be toxic to aquatic organisms. Never use it as an improvised solution in a fish pond. The term mineral does not mean risk-free.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Natural swimming pool with plants

A natural swimming pool works through circulation, microbial biofilms, filters, and sometimes a planted zone. A chlorine shock can destroy beneficial bacteria. Do not add chlorine, bromine, copper, or unapproved algaecide. Remove deposits, check nutrient levels, and maintain the filters according to the designer’s instructions.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

Natural swimming pool without visible plants

Some natural pools have hidden biofilters and look like conventional pools. The absence of plants does not mean chlorine is allowed. Check the plans and instructions. Algae may result from excess nutrients or poor circulation. Do not destroy the biofilter with an improvised treatment.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

Swimming pond with fish

Never pour shock chlorine, bromine, or pool copper into a pool containing fish. Check oxygen, pH, nitrites, and ammonia/ammonium. Observe the fish: gasping or abnormal behavior requires urgent evaluation. Remove algae gradually. The presence of fish also raises health concerns for swimmers.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

Natural pond without fish

Even without visible fish, a pond is home to amphibians, invertebrates, bacteria, and sensitive plants. Control nutrient inputs, sediment, and runoff. Remove filamentous algae gradually. If a cyanobacterial bloom is suspected, suspend swimming and have the phenomenon identified. Do not use improvised algaecides.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Pool with submerged wood

Distinguish a wooden frame behind a liner from wood that is actually submerged. Fibers and gaps can sometimes retain biofilms. Use a compatible soft nylon brush, then vacuum up the deposits. Avoid metal, aggressive pressure washers, and concentrated products. Do not sand or varnish without the manufacturer’s approval.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Liner, reinforced PVC, and shell

Each surface covering has its own cleaning constraints. A concentrate can discolor a liner, and an abrasive brush can scratch a gelcoat. A green stain may also be metal discoloration. Consult the instructions, test a gentle method, and check circulation. The surface covering does not reveal the disinfection system.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

Concrete, stone, and tile

Joints, pores, and microcracks can retain deposits. Some stones are sensitive to acids, and some joints to harsh cleaners. Use compatible accessories and avoid chemical mixtures. A concrete pool may operate with chlorine or biologically: the material does not determine the permitted treatment.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

Above-ground and tubular pool

Small volumes can sometimes experience rapid changes in temperature and organic load. A dosing error is particularly significant in these settings. Measure the actual volume, water quality, and filter capacity. Clean surfaces with compatible accessories. Never apply a dosage intended for a large pool to a small basin.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

Spa and Nordic bath

High temperatures, jets, and plumbing can promote biofilms. Sanitary maintenance for a spa differs from that of a large pool. Check the instructions, specific parameters, and the condition of the pipes. For a wooden Nordic bath, also check material compatibility. Do not repurpose a pond product.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Shared or guest pool

A pool open to customers or the public may be subject to stricter health requirements. Green water should trigger an operating procedure, not a generic recipe. Close access if the parameters are not under control and consult a qualified operator. Regional rules and documented inspections take precedence over general advice.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Green algae, filaments, and black deposits

A green, slippery surface may be algae or a biofilm. Filaments form clumps; brown or black deposits may have several origins. A photo can help without guaranteeing identification. Some cyanobacteria can produce toxins. If suspected, keep children and animals away and suspend swimming.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

Mechanical cleaning and vacuuming

Start by removing leaves and large deposits. Brush with a tool compatible with the material, then vacuum up the loosened particles. Clean the baskets and prefilters. Check corners and stagnant areas. For a natural swimming pool, take care to preserve beneficial bacterial substrates. For a conventional pool, then check the disinfection parameters.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

Preventing and controlling recurrence

The return of algae often signals a persistent cause: insufficient circulation, nutrients, embedded deposits, or poorly controlled disinfection. Record measurements, temperatures, and cleaning dates. Pay particular attention to steps and gaps in the wood. A lasting solution depends on consistent maintenance, not on accumulating products.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

Dangerous mistakes to avoid

Never pour shock chlorine into a natural swimming pool or fishpond. Do not assume that a saltwater pool is chlorine-free. Do not confuse hydrolysis with biological filtration. Never mix acid, chlorine, and oxidizers. Do not use an algaecide for an ornamental pond in a swimming pool without explicit compatibility.

Before adding a product, precisely identify the system, volume, and materials. Check the instructions and measurements appropriate for your technology. A recommendation intended for a chlorinated pool may be dangerous in a natural swimming pool or for fish. If in doubt, refrain from adding a biocide.

Physical cleaning, filtration checks, and identifying poorly circulated areas are often useful steps, but accessories must be compatible with the lining. Avoid aggressive brushes and local applications of concentrated products. If the deposits persist, have the installation inspected.

To prevent recurrence, control organic matter, leaves, sediment, and circulation. Monitor the parameters specific to your pond, without applying a universal value to all systems. Document the results over several days to understand changes rather than multiplying treatments.

A professional can confirm the nature of the deposits, inspect the equipment, and recommend a protocol that complies with the manufacturer's requirements. Do not swim in water that is cloudy, suspect, or whose sanitary parameters are not under control. The protection of people and aquatic life must always take priority over aesthetics.

To identify the cause, note the appearance of the deposits, their location, how quickly they reappear, and previous interventions. A green surface is not always proof of insufficient disinfection. The technical context matters just as much as the color. Clear water is not a guarantee of microbiological safety.

Useful equipment for removing deposits

Pond vacuums can help remove loosened matter, subject to compatibility with the lining and installation. They do not replace water analysis and are not a chemical treatment.

Discover the PondoVac 5 and the PondoVac 4.

Frequently asked questions

Can chlorine be added to a natural swimming pool?

No, not in a bathing system designed to operate without chlorine disinfection, except under an exceptional procedure explicitly approved by its designer.

Can a saltwater pool develop algae?

Yes. Measure the free chlorine and check the cell, filtration, and pH.

Is a hydrolysis pool chlorine-free?

Not necessarily. It depends on the exact technology and the associated equipment.

Can a pond algaecide be used in a swimming pool?

Only if the manufacturer explicitly authorizes its use in swimming water and confirms its compatibility with the installation.

Foudebassin: prioritize diagnosis, prevention, and compatible equipment before adding any treatment.