Commonly used algaecides
Quats
Quaternary ammonia compounds (quats), typically alkyl dimethyl benzyl ammonium chloride, are organic based “cleaning” type algaecides. These algaecides have a surfactant quality to them that may cause them to foam, especially in the presence of aerated water. Regardless of the visual results of their addition, these algaecides are effective as a killer on contact, as they disrupt the cell membranes. However, quat-based algaecides do not have much staying power in water compared to other liquid algaecide products, especially in the presence of higher levels of chlorine.
Polyquats
The other non-metal algaecides used in pool water are polyquats, typically polyethylene dichloride. Unlike quats, these algaecides do not foam. They are effective at clarifying pool water and work on a broad spectrum of algae. Since these algae preventers work by essentially encapsulating algaecide (part of the reason why they are good clarifiers), the potential working effects of this chemistry could be impeded by any common debris present in the pool. Polyquats have good staying power in the water for a liquid product, usually a week or two, and are fairly chlorine tolerant.
Metal-based algaecides
Copper
The most common metal-based algaecide utilizes copper. Copper products are both algaecides and algaestats and are effective on all types of algae. Since they can also be considered fungicides and bactericides, they can be effective against bacteria such as “pink slime.” Effectively chelated copper algaecides can last a longer time in water without causing issues, especially if the ideal water balance levels are maintained. Since copper poisons pool algae, its efficacy is slow, but very high. It also has the potential to discolour bathers’ hair and plaster surfaces with a blue-green colour if it precipitates out of solution. In present-day applications, copper products are one of the lower cost algaecides. When adding metals to pool water, the effluent waste should never be discharged into ponds, streams, or similar water.
Silver
At the time of this publication, silver is currently trading for around $22 for 28.3 g (1 oz). Although not much is needed in order to be effective,
silver algaecides are among the higher priced
algae treatments. This metallic algaecide and bactericide has a similar staying power and killing mechanism to copper algaecides. Silver algaecides products are effective against black algae and “pink slime.” However, similar to copper algaecides, they do not fare well with salt chlorine generators.
Algae-destroying adjuncts
Sodium bromide (NaBr)
While it is not considered one by itself, sodium bromide is used like an algaecide. It introduces bromide ions to the water, so they may be oxidized or changed into hypobromous acid—the killing agent of bromine. Hypobromous acid is a highly effective destroyer of algae.4 However, if used by itself, it cannot be stabilized and is lost quickly in the water. Sodium bromide also creates an oxidizer demand in the water which can take days or weeks to resolve. Minimal dosing is recommended, and it is best used with minimal physical presence of algae, typically spot blue-green algae, and mustard yellow algae. As a side note, bromine (BCDMH or DCDMH) itself should be considered for daily use if algae is a common occurrence in the pool.
Ammonium sulfate ([NH4]2SO4)
Ammonium sulfate is another chemical compound thought to be an algaecide, even though it is not. Ammonium sulfate is an inorganic salt used as a fertilizer in other industries. In pools, it is used as an accelerant for algae. After the chemical is applied to water, the algae divide rapidly, and become more vulnerable to treatments. Since a pool professional would add chlorine at the same time, they would rid the pool of the algae instead of creating more. Using this chemistry often requires pH adjustments before and after treatment. Several kilograms (pounds) of oxidizers are also needed to treat even smaller bodies of water.
