What is Algae?

Algae is an informal term for a wide variety of photosynthetic organisms that are not necessarily closely related in the animal kingdom. Many types of pool bacteria are erroneously referred to as “algae”. In the pool industry, it is often attributed to visible “blooms” or colonies of microorganisms growing in a pool.

There are thousands of species of “algae” that may grow in pools. For purposes of pool maintenance, algae tends to be classified according to color: yellow (a.k.a mustard), green, black, and pink.

Can pools get mold and/or fungus?

While there are several things that grow in pools that are often referred to as “mold”, fungus technically doesn’t really grow in pools (with one exception that we will talk about at the end). Usually what’s being referred to as a mold is really a type of algae or bacteria. 

How does algae get into the pool?

Microorganisms are introduced to pools in a variety of ways; wind, rain runoff, cross contamination of pool equipment, swimmers, etc. Often, multiple species of the above mentioned microorganisms are present in a pool at any one time.

The combination of your sanitizer (i.e. chlorine) and filtration equipment typically keeps them in check.

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Yellow/Mustard Algae

Yellow/Mustard Algae is the most common form of algae in swimming pools. This type of algae is most commonly found in the sunbelt states from Southern California to Florida.

Typically, mustard algae grows along the walls in the areas of the pool with the least direct sunlight. It brushes of relatively easily, but can quickly return to the same areas. This is because Yellow Algae has flagellates – small tendrils that wave as a method of transportation.

Like most algae, mustard algae tends to show in the warmer summer months when water gets warmer and sanitizer burns more quickly.

Green Algae

Green Algae is the second most common form of algae in swimming pools. And is synonymous for having a “swamp” pool. It’s more common in more seasonal and humid climates – such as the South East and North East US. 

Green algae tends to grow on the walls, but in severe cases can form “patties” on the surface of the water. The algae itself tends to grow denser and in longer tendrils than mustard algae.

Green algae tends to grow when the water gets warm and there’s a lack of sanitizer. This makes it a common problem when first opening a closed pool in the spring.

Black Algae

Black algae is often described as the toughest algae to kill. Black algae is actually cyanobacteria, similar to what’s referred to as “black mold” around the home.

Black algae tends to grow on porous surfaces with the least circulation. This means you’ll commonly find it in corners and around steps where circulation is lowest. Like other algae, it also prefers shadier areas of the pool. But don’t be surprised to find it in other areas where the surface may be etched or rough.

Biologically, black algae differs quite a bit from other algae. It tends to grow in longer filaments that “wave” as a means of propulsion. They also have thick gelatinous walls that make them much tougher to kill using sanitizer. This is why most treatments require vigorous brushing – to damage the cell walls enough to allow sanitizer and algicide to attack the cell.

Another important distinction between black algae and other types of algae is that they release “Akinetes” – a special type of spore invisible to the naked eye. When they feel attacked, they responded by releasing  thick walled dormant cells that are virtually impossible to kill. Even being able to survive acid washing.

Once the water environment returns to habitable conditions, these cells become active again to grow more black algae. This means that once a pool has had black algae, it will be prone to having it again.

Pink Algae

Pink algae is a very specific type of bacteria of the species Serratia. It appears as a pink slime growing in stagnant areas of water outside of direct sunlight. It’s also known to grow underneath fixtures and behind pool lights. 

Pink algae or pink slime is relatively rare in chlorine sanitized pools, but is slightly more common in pools sanitized with hydrogen peroxide (such as those treated with Baquacil or Biguanide). In either case, some of the bacteria enters the water during low sanitizer conditions, and grows quickly. The large amount of biomass can hit a tipping point where sanitizer can no longer keep up – even at normal levels. Treatment requires exposing as much of the bacteria to a strong algicide at once. This often requires physical scooping and brushing the bacteria into the water. Also you should treat or replace any items used in the pool to prevent re-contamination.

It’s important to note that Serratia is a human pathogen as well. This means the bacteria can lead to infections. You should take care to cover any open wounds or sores when dealing with pink slime.

White Water Mold

White water mold is a type of algae related to the more common mustard algae. However, unlike mustard algae, white water mold prefers to grow on the surface of the water and is more off-white in color. Many people describe it as looking like “shredded tissue paper”.

Like most of they types of algae, it appears in humid areas with warmer water and when sanitizer levels are allowed to get low. 

What can make water mold difficult to kill is that it often grows on the surface of the water. Granular and heavier-than-water liquid chemicals tend to be at higher concentrations deeper in the water (at least initially – when they have the most chemical energy). Chemicals at the water level are exposed to more UV light and break down quicker. This means that less of the algae itself is exposed to sanitizers and algicides while growing on the surface. 

Vinyl Fungus

Vinyl fungus is one of the rare instances you may encounter a true fungus in your pool. It usually begins as a dark colored stain at the bottom of the liner before spreading across the pool. It’s often confused for black algae as they tend to look very similar in appearance. A way to distinguish the two is if the growth is contiguous (it’s all connected) and is on the bottom of the liner, it is likely vinyl fungus.

The fungus itself comes from underneath the liner. In areas with high water tables, the soil underneath the vinyl pool remains damp. This cool, dark, damp environment is ideal conditions for fungi to grow. The fungus then begins to grow through the microscopic holes in the liner to the water.

The main difficulty in treating vinyl fungus is that it’s originating from underneath the liner. The only true way to treat it would be to remove the liner and use a fungicide to treat the ground underneath.

Alternatively, you may be able to keep the fungus at bay by treating only what is visible on the vinyl surface, increasing sanitizer levels and using a strong preventative algicide.

Conclusion

While there is a large variety of things that you may have growing in your pool, eliminating and preventing algae is pretty straight forward:

1. Eliminate the algae using a strong algicide
2. Maintain proper santizer levels
3. Use a preventative algicide to keep it from coming back

If you’re struggling with any of these problems, feel free to open a support ticket and we’ll be happy to diagnose your problem for you and advise on the best way to solve it.