String Algae vs Hair Algae – What’s the Difference?

Whether you’re into aquariums, swimming pools or fish ponds, you’ve likely encountered many types of algae. Some, make the water look cloudy. Others, look like weeds or grass growing on top of other plants.

There are thousands of species of algae in the world. If you’ve been around aquatic environments for any length of time, you’ve probably heard the terms “string algae” or “hair algae”. Have you ever wondered what the difference is? Are they the same thing? Are they at least closely related?

Here is a brief summary of String Algae Vs. Hair Algae: String Algae grows horizontally in sheets (blankets). Some might call it Pond Scum. Hair Algae is usually found suspended in water or attached to things like “slippery rocks” It looks fuzzy and blurry under water.

But honestly, there is so much more to these algaes so please read on for the full discussion and to learn how you may have gotten these algae blooms in the first place.

What are Algae?

In a nutshell, the term “algae” refers to a broad spectrum of aquatic organisms. They can be single-celled or multi-celled. Algae grow in ponds, lakes, rivers, streams, indoor aquariums and even swimming pools. They can make the water look cloudy by presenting as floating particles, or they can look more like weeds, strings or other plants.

Algae Characteristics – All Classes

Does Algae Have Roots?

The majority of algae species do not have roots or stems that grow down into the Earth like land plants. Instead, they attach themselves to leaves, rocks and other structures in the water. They appear in a range of sizes from a couple micrometers to nearly 60 meters in length.

How Algae Eats

Algae have the ability to take sunlight and turn it into food through the process of photosynthesis. This basically means they can make carbs out of sunlight! The process also involves carbon dioxide and oxygen but in general, they create their own nourishment using light energy.

Does Algae have a Purpose?

In fact, algae are an extremely important part of our ecosystem. They produce nearly half of the oxygen in the Earth’s atmosphere. The process of photosynthesis creates oxygen as a bi-product, which contributes directly to our air quality and environment.

Alga also serve as a food source for many species of fish and other aquatic life. Baby fish and tadpoles often take shelter in the algae, as well.

Why are Algae Problematic?

Despite their positive contributions to the environment, algae get a bad rap for making swimming pools and aquariums turn green and for creating an ugly film in ponds, lakes and streams.  A small amount of algae is usually healthy for natural aquatic environments, but an infestation can become a serious problem if left unattended.

Algae Infestation

The technical term for an infestation of algae is an algal bloom. An algal bloom refers to an overgrowth of algae that disrupts the balance of an aquatic environment. It does so by growing rampantly, which results in the production of toxins that can harm the environment.

Typically, when an algal bloom happens, it is because there are too many nutrients in the water. This seems counterintuitive, but it’s true. Too much nitrogen and phosphorous can cause the overgrowth of algae. More often than not, the high levels of nitrogen and phosphorous are caused by human activities, rather than natural activities. An example of such an activity would be the run-off manmade chemicals or fertilizers that end up in the water.

Many gardeners have been shocked to find algae in their gardens just weeks after adding nitrogen.

An algal bloom can cause damage to the aquatic environment in many ways. They can produce toxins that kill other plants and aquatic life. They can also kill other plants because they are competing for sunlight and nutrients. If the algae become too large, they will take the majority of those resources, causing other species to die.

String Algae vs Hair Algae:

Let’s get a little more specific about what you might be dealing with in your own aquatic environment. Here is a breakdown of the basic differences between string algae and hair algae.

String Algae

String algae are known scientifically as claudophora spirogyra. They are sometimes referred to as blanket weed or pond scum because they can float on top of the water and look like a blanket. They are multicellular and photosynthetic.

String algae are typically found in shallow lakes and streams. They can also be found in koi ponds, water gardens and other water features. They grow in both freshwater and brackish water. They typically attach themselves to rocks, plants and other structures in your pond or water feature. Once attached, they grow in length and thickness.

They look like a fibrous tangled mess or they can have nice, even horizontal lines running through them.

While they are always present in our aquatic environments, they typically go unnoticed until there is an algal bloom. Once they bloom and become overpowering, many pond keepers find it necessary to take action to stop them. As discussed earlier, an algal bloom can be very invasive and cause other organisms in the pond to die due to toxins or a lack of nutrients or sunlight.

Hair Algae

Hair algae are known scientifically as Oedogonium. They are an exclusively freshwater species of algae. They are unicellular and photosynthetic.

They are most commonly found in quiet outdoor environments and freshwater aquariums. Much like string algae, they attach themselves to plants and other structures in the water. However, they are typically much shorter than string algae. They tend to look like fur growing on the leaf of a plant as opposed to long blankets of strands like string algae. They can also float freely in the water.

Much like string algae, hair algae usually appear when there is an imbalance of nutrients in the water. Whether it is a natural environment outdoors, or an aquarium indoors, the nutrient imbalance can cause the growth of algae to become too large. For this reason, it is important to maintain the water quality of your aquatic environment.

In the case of freshwater aquariums, it is also important to have enough algae eaters in your tank. These species of fish and other aquatic life will feed on the algae. This can help keep the tank clean and free of algal blooms.


String algae and hair algae are definitely two different species. They can look very similar, but require slightly different conditions in order to bloom. Algal blooms in both species can be caused by an imbalance of nutrients in the water. These imbalances are often caused by human activity, rather than naturally-occurring phenomena.

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