All About the Water: Algae, Yuck!

There are close to 50 species of clean-water algae. This means that over the course of time, you might see 50 different forms of algae in your pool or spa. (We sure hope they won’t all be there at once!) Because of the many types of algae that might be present, there is a wide variety of algaecides available. This is because some algaecides work better on one kind of algae than on another.

Some algae attach themselves to the rough spots on the walls and floors of the pool or spa; these little devils can be a pain to remove. Other types float on the surface of the water. Still others behave somewhere in between the other two kinds. They also come in different colors: yellow, green, blue, brown, pink, black or tie-dyed (OK, maybe not tie-dyed).

Many factors can also contribute to algae growth. For example, high temperatures can increase the rate at which algae grows. The higher the temperature, the faster the algae will grow and multiply. Sunlight is also an important factor. Algae requires some light to be able to grow, and bright sunlight tends to accelerate algae growth. Heat and sunlight for algae are like dry twigs for a fire.

The pH, bacteria and mineral content of the water can also affect the presence of algae and the growth rate. Proper levels will help to prevent a bloom of algae in your water. (When algae forms it is often referred to as an algae “bloom”.) A pool can go from clean to green (or some other color) in a period of 24 hours under the right (wrong?) conditions. And it can take a lot longer to treat and get rid of algae once it becomes established.

Treating Algae

There are two times that we treat algae. First, we treat the water so that it prevents the formation of algae. And second, we treat the water after an algae bloom has occurred.

Prevention

The best prevention for algae is to have a chlorine or bromine sanitizer level that is sufficient to kill contaminants. Sources of algae-forming contaminants include dust and other wind-borne debris, rain, falling leaves, or even the source water used to fill the pool or spa. As long as you maintain chlorine or bromine at the right level, you usually do not need an additional algaecide.

Many pools are more susceptible to algae problems due to the surrounding environment. For example, spring blossoms blowing into the water and leaves falling down in autumn can contribute to a significant algae problem. Under these conditions, your chlorine and bromine may be consumed rapidly. In this kind of situation, having a preventative algaecide may save your pool from an algae explosion.

All other sanitizing systems that do not maintain a high free chlorine or bromine residual will also require some kind of algae prevention chemical. There are several chemicals you choose from to do this job. However, each system will usually recommend a different chemical.

Types of Algaecides

Quaternary Ammonium Salts

The most widely used algaecide contains the active ingredient of quaternary ammonium salts (for example, Alkyl dimethyl benzyl ammonium chloride). This is a good algaecide for preventative maintenance in pools and spas where chlorine and bromine levels are not sufficient. It is also a smart choice where algae problems have been known to occur. This is the chemical of choice for the biguanide sanitizing system. It is most effective against green, blue-green and black types of algae.

You can also use this chemical if there is already algae in the water. However, some experts agree that it is not as effective killing algae that is already present. You will require a larger dosage amount for an existing problem. This will kill the algae, and will usually drop it to the bottom and sides of the pool. Afterwards you will have to undertake a thorough cleaning to ensure the problem has been eliminated.

Poly Quats

Another commonly used algaecide is what we refer to as poly quats (for example, Poly[ethylene dichloride]). You can always recognize this type of algaecide by the “poly” as the first term in the active ingredient. This indicates that the active ingredient is a polymer--a chain of millions of linked units of simple molecules.

Poly quats are a different chemical than the quaternary ammonium salts we described above. The active concentrations are different as well; they are often used in smaller dosage amounts to treat algae. They are most effective in treating green and black algaes. In addition, you can use poly quats for killing algae when it is already present in the water. Like all other algaecides, you have to clean the pool or hot tub thoroughly after an algae bloom.

Algae Treatment

When an algae bloom has already occurred in the pool or spa water, there will be a different treatment required. At a minimum, you will need a larger dose of algaecide in order to destroy the visible algae. You may have to select a specific chemical to eliminate a certain kind of algae. If there is so much algae in the pool that it looks safe to walk across, you will need an even larger dosage of algaecide.

Once again, there are several chemicals available for killing existing algae. Remember that poly quats and quaternary ammonium salts will work, as we discussed earlier in this section. Here are some alternative chemicals:

Copper-Based Algaecide

Copper-based algaecides contain copper as an active ingredient to destroy algae. (Bet that surprised you, considering the title of this section.) Usually the concentration is around 7% active copper. This compound is most effective in killing yellow/mustard algae and green algae.

You should remove any metals from the water prior to adding this chemical: it will introduce additional metal in the form of copper. If there is already high metal content in the water, the copper will come out of solution and stain the plaster, liner and equipment.

For the same reason, you should not use this chemical in mineral purification systems. They utilize copper and silver to sanitize the water, and you do not want to add any extra copper.

Copper-based algaecides are incompatible with biguanide/hydrogen peroxide shock systems as well. Metals have a greater tendency to stain in the biguanide/peroxide shock system. This chemical is not frequently used as a routine algaecide since it increases the metal levels of the water. You need to add a metal agent to the water after copper algaecide treatment to prevent staining from the copper.

Yellow/Mustard Algae Treatment

Some companies make a chemical that helps to specifically remove yellow/mustard algae. The active ingredient is usually ammonium sulfate along with other additives. This is not an algaecide by itself. It is designed for use in coordination with chlorine to intensify its algae killing ability. This chemical only works for treating yellow/mustard algae. You may use it routinely if this type of algae bloom frequently occurs.

Others

Colloidal Silver can spot-treat algae and eliminate black algae. Once again, you must take precautions to ensure that no other metals are present in the water. You should not use this in mineral purification or biguanide systems. Many chlorine compounds can also treat algae. They are effective in destroying algae, although you may have to add large doses. Ordinarily you employ a fast-dissolving chlorine compound to treat the algae quickly. A slow-dissolving chemical may not act quickly enough to destroy all the algae and keep it from growing. Slow-dissolving compounds may be a good “spot algaecide” when algae is localized in one specific, small area of a pool.