The EPA doesn’t exert much control over most specialty chemicals, but when it comes to making claims to be an algicide, it must be registered and approved as such with the EPA. To be classified as an algicide, the chemical must undergo thorough testing procedures to ensure the chemical’s safety and efficacy. Algicides and algestats come in several forms. The most common include quaternary ammonium compounds and polymeric quats.
Quaternary ammonium compounds, “quats”, are positively charged nitrogen-based compounds. They have a positively charged nitrogen head and a carbon chain tail. Since the cell membrane of algae has a negative charge, electrostatic forces attract the nitrogen to its surface. Ultimately, many of these molecules are attracted to the algae cell , surrounding it. They work by disrupting the algae’s cell membrane. The molecule is shaped like a surfactant and like soap, they can get sudsy, so they are unsuitable in spas. Also, their positive charge attracts dirt and like a clarifier they can end up in the filter. Quats are a good preventative step against algae.
Polymeric quats, or polyquats are similar to quatemary ammonium compounds, but they have a much larger molecule structure, made of repeating carbon-based groups. They were designed to reduce the foaming issue. They are much larger molecules than quats so they work a little slower. Polyquats are a good preventative step against algae. Copper-based formulations are among the more common Algicides because they are effective against many types of algae. Some of the registered copper algicides include copper sulfate, and copper ethanolamines, or triethanolamines. The chelated forms help prevent the copper from staining surfaces, which can happen with copper salts like copper sulfate. Copper-based products disrupt cell division and cause electrolyte leakage from cell membranes.
Copper algicides are effective on green and mustard types of algae. They tend to work best at slightly elevated pH’s: 8-8.4 is a good target. One of the major disadvantages of using copper products is that they can cause staining over time, as chlorine or other oxidizers break down the chelating agent. While this doesn’t matter as much for vinyl-lined pools, it is of greater importance for plaster pools. When adding any chemical, it is important to carefully follow the direction. When using copper-based algicides, staining can occur if copper concentrations get too high, even if the copper products contain chelators or sequestrants. Chelated copper can be stable for a few months, but ultimately the chelator can break down, allowing the copper to precipitate out. The first sign of this is blue or green water, which is often misidentified as an emerging algae bloom. However if there is no appreciable change in chlorine demand, it is likely to be copper. Silver-based algicides are also effective against algae. They work by interfering with metabolic activities. This algicide comes in the form of colliodal silver, or silver particles suspended in a liquid. Silver algicides are often recommended for fighting against black algae. They are not generally recommended as preventatives but rather as curatives because the sunlight can cause the formation of silver oxide, which is black and stains surfaces. Also, they are expensive, and can be difficult to find. One EPA-registered aglaestat , sodium tetraborate, is a carbon dioxide scavenger. This compound works by depriving algae of carbon dioxide, which it needs to support life. Though It has its uses, it is a good idea to remember that since water is continually exposed to the atmosphere, carbon dioxide will eventually return.