Which of the following is NOT listed as a method to control filamentous algae?

• A. Mechanical Removal
• B. Addition of Desired Plants and Good Filtration
• C. Non-Toxic Dyes That Filter Out Sunlight and Starve the Algae
• D. Ultraviolet Light Disinfection

Answer: (D)

Filamentous algae bloom is driven by light availability and nutrient levels, and the most effective management approaches target those factors: reducing sunlight reaching the algae (for example, with shading dyes), promoting competition from desirable plants, and maintaining good filtration to limit nutrients, plus physically removing mats when they appear. Ultraviolet light disinfection is mainly used to inactivate pathogens in water and is less reliable for filamentous algae because those algae form dense, attached mats that UV light can’t penetrate well; the water also often isn’t clear enough for UV to be effective. In practice, UV treatment isn’t a standard method listed for controlling filamentous algae, whereas the other strategies directly address the conditions that let the algae thrive.