When applying crystalline copper sulfate to control filamentous algae, what is the recommended method?

• A. Crystals should first be dissolved in water, then sprayed onto mats.
• B. Dry crystals should be sprinkled directly on the mats.
• C. Crystals should be dissolved in sediment.
• D. Apply only at night.

Answer: (A)

Delivering copper sulfate in a dissolved, sprayable form ensures the algae mat is exposed evenly and at a known, controllable dose. When crystals are dissolved in water and sprayed, the active copper ions contact the filamentous algae more uniformly, improving effectiveness and reducing the risk of creating very high local concentrations that can harm non-target organisms or accumulate in sediments. Sprinkling dry crystals directly on mats tends to produce patchy exposure and can leave undissolved particles that are less effective. Dissolving in sediment is inappropriate because copper can bind to sediments and persist there, reducing contact with the algae and increasing benthic exposure. Applying only at night does not address how the product is delivered; the key point is delivering a solution that reaches the algae rather than relying on dry materials or sediment interaction.