Help create the ideal home for your freshwater fish with the API Water Softener Pillow. Most people don't think about their drinking water as "hard" or "soft"—but fish do! In fact， the right kind of water is essential to their health and comfort. And different species of fish need different levels. That's because hard water contains a considerable amount of dissolved minerals—like calcium and magnesium—while soft water only contains sodium. Once you know what your fishies need， this water softener from API will help to remove calcium， magnesium and soluble heavy metal and soften your water. The convenient pouch is fully rechargeable and can be used multiple times， too!