As the research progressed into the effective eradication of green algae, it became evident that while Chlorella is easily killed by chlorine, quaternary (quat) or polyquat-based algaecides, and copper-based algaecides, Scendesmus acutus exhibited lower susceptibility to low copper residuals. Has one ever used a copper-based algaecide and expected it to clear the pool quickly, only to discover that it proves ineffective in combating the algae growth? In such scenarios, even repeated applications may not yield better results. The green algae in the pool could, in these cases, be Scendesmus acutus, opposed to the more commonly encountered Chlorella. Unfortunately, differentiating between the two at the poolside is not feasible.
Unveiling the mustard algae secrets
Further, this research delved into an extensive examination of mustard algae. The most common type found in a pool is known as Eustigmatos vischeri. This algae displays a yellow hue and exhibits the common characteristics associated with mustard algae, such as settling at the pool’s bottom, able to be brushed, and presenting control challenges. The image of Eustigmatos vischeri provides insight into why it can be difficult to treat in pool water. As depicted, this algae species is round and appears to be covered by a hard outer shell. This shell can make some species of Eustigmatos more resistant to chlorine, necessitating elevated chlorine levels for effective control. However, copper-based algaecides are highly effective against mustard algae because they are ingested into the algae cell, bypassing the need to breach the outer cell wall.
In the process of classifying mustard algae, real world pool samples yielded a different species that looked like mustard algae in the pool but was an entirely distinct organism. On the surface, it appeared to be Eustigmatos vischeri, however, it was actually Nitzschia communis (Figure 2).
Nitzschia communis is a diatom that presents as mustard algae but is a completely different organism. It has flagella and is capable of independent movement within the water. It primarily feeds on silica to enhance the reserves needed for its survival. In a pool environment, a continuous supply of silica is offered to these diatoms through a sand filter or other dirt and debris from the pool’s surrounding environment, enabling them to grow and reproduce. In many cases, recurring mustard algae outbreaks in pools can be attributed to the failure to chemically clean the filter following an algae treatment.
If Nitzschia communis is growing in a pool, not cleaning the filter will allow it to persist and reproduce even after treatment. Consequently, the entire pool is susceptible to reinfestation, perpetuating the cycle. Thoroughly cleaning the filter with chemicals after an algae outbreak is a critical component of the treatment process. In addition, the presence of dirt (which contains silica) in poorly circulated areas at the bottom of the pool can lead to an environment where conducive to the growth and reproduction of Nitzschia communis.
