Hydrothol is toxic above which concentration?

• A. 3.0 ppm
• B. 0.03 ppm
• C. 0.3 ppm
• D. 0.003 ppm

Answer: (C)

Copper-based Hydrothol releases copper ions into the water, and these ions become toxic to fish and other aquatic life as their concentration increases. The concentration at which Hydrothol becomes toxic is about 0.3 ppm. So when the water is around or above this level, the risk to aquatic organisms rises; below this level, toxicity risk is lower under typical conditions. Remember that factors like water hardness, pH, temperature, and exposure time affect how toxic copper is—soft, acidic water makes copper more toxic, while hard, alkaline water reduces toxicity. Always follow the label, test the water, and avoid overdosing.