Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 132

One of the biggest issues with outdoor ponds is phosphates and sunlight causing algal and bacterial blooms. These are particularly dangerous when the biological oxygen demand (BOD) is high (e.g. in a heavily stocked system or at night when photosynthesis is not active). In these situations, a bloom can lead to life‐threatening hypoxic events. These can be minimized using shade and by controlling phosphates and potentially nitrogen and iron levels. Phosphates and nitrogen build up through the introduction of food and other organics into the system. Input can be limited by regular removal of decaying matter (e.g. leaves), covering with nets in the fall, and only feeding to appetite. In the system, they can be managed with chemical flocculation (e.g. precipitation with lime, lanthanum chloride, aluminum sulfate, or iron salts). Metallic flocculants work well, but some (e.g. lanthanum salts) produce flocs that must be prevented from entering the pond as they can disrupt gill function in fish. Aluminum sulfate is one of the most commonly used, but care should be taken when applying as it will decrease pH.