Stress Zyme – 3.8L. STRESS ZYME contains over 300 million live bacteria per teaspoonful. Breaks down organic compounds that cause dangerous conditions such as ammonia and nitrite poisoning and low oxygen levels. These bacteria improve the development of the biological filter and help clean a dirty aquarium. Making STRESS ZYME a part of regular care assures an active biological filter, cleaner aquarium, healthier fish and good water quality. No refrigeration necessary.