What are bio balls used for???
Bio balls typically float. You can submerge them but the water should be well areated. They provide large amounts of surface area in a small space so that lots of beneficial bacteria can form on the surface. They float so that this area can be close to the air so the bacteria get oxygen they need to thrive. These bacteria convert ammonia and harmful nitrites into less toxic nitrates. This helps the water quality. In large quantities, Nitrates can also poison fish. They are removed partly by activated carbon in your filter, and most importantly when you change the water of the tank. Bio balls are useful when you have them inside of a large filter like a canister filter or a sump, and if you maintain them in an established tank they can be used later to help you quickly establish healthy bacteria levels in a new tank.
