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Identifying and Treating Algae in Pools

Identifying and Treating Algae in Pools

There are over 400 types of algae that can be found in water.

In general, the pool industry puts them into three major categories: green algae, yellow algae, and black algae.

  • Green algae is the type you see in the water itself, it makes the water look like "pea soup". If the water is looking cloudy, chances are you are about to have problems with green algae.
  • Mustard algae is very common, even in well-maintained pools. The water itself will be clear, however the algae will grow on walls - usually starting in shady areas. It brushes off fairly easily (often described as a "cloud") but usually returns quickly.
  • Black algae are small spots on the walls or bottom of the pool, and can be confused with mold/mildew. In general black algae will not grow if free chlorine levels are maintained in the pool.

Preventing algae growth is much easier than treating it. Algae requires phosphorus in order to grow & thrive, so keeping phosphate levels low will make your pool inhospitable to algae.

Keep phosphate levels low (below 350ppb) using Orb-3 DropOut or Orb-3 PRA & Enzymes Maintenance; and treat with Orb-3 Pool Enzymes to prevent the formation of scum lines and bio-films, which nourish & protect algae.

Algae that form on surfaces tend to have a protective layer that makes them difficult to kill without brushing. Use Orb-3 Enzyme Cleaner to remove that protective layer, thereby exposing them to the treatments, and to help make brushing easier.

Here are some recommendations for treating the various types of algae blooms:

Green Algae

  1. Shock your pool with chlorine.
  2. Run the pool pump for up to 24-hours.
  3. If the pool is already green, treat with an algaecide. "Algaecide 60" is a common choice for treating green algae. This is not an Orb-3 Product.
  4. Test chlorine levels regularly and add chlorine if necessary.
  5. Monitor filter pressure.
  6. If you notice algae forming on the walls or floor of the pool, brush them to remove the algae.

Mustard Algae

  1. Brush pool surfaces to remove the algae.
  2. Shock your pool with chlorine to get chlorine levels above 5ppm.
  3. Treat with an algaecide. "Algaecide 60" is a common choice for treating mustard algae & most of the time successfully takes care of the problem. This is not an Orb-3 Product.
  4. If the algae returns after using "Algaecide 60", shock & brush the pool again & this time use a "copper" algaecide. Follow the directions carefully - beware that copper is not friendly & can cause staining. A sequestering agent may help prevent staining. Orb-3 does not manufacture a copper product nor does it manufacture sequestering agents.

Black Algae

  1. Use a brush to scrape the head off of the algae & expose it to the chlorine & algaecide in the water.
  2. Raise chlorine levels to at least 5ppm.
  3. Add "black algae killer" or a "copper" algaecide to the pool water. These are not Orb-3 Products.
  4. Run the pump for at least 24 hours.
  5. Test chlorine levels regularly and add chlorine if necessary. Black algae does not usually form if there is sufficient chlorine in the pool.


Once the algae is under control, prevent it from returning:

  1. Test your pool for phosphates.
  2. Use Orb-3 DropOut for phosphate levels over 750ppb.
  3. Use Orb-3 PRA & Enzymes Maintenance for phosphate levels between 350ppb and 750ppb.
  4. Use Orb-3 Pool Enzymes if phosphate levels are below 350ppb.

Always monitor & maintain free chlorine levels to ensure clean & safe water.

If you are in the market for a home with a pool, this article Is Owning a Pool Right for You? What You Should Know Before You Dive In is a helpful resource.

Information on products not manufactured by Orb-3 is provided as-is and without warranty. Follow all label instructions thoroughly and contact the manufacturer or a service professional if you have any questions.

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