When adding media to our filter systems, it’s a good idea to know how the media works before putting it into use. Some media can be tumbled violently, while others need to remain very still. This is due mostly to the fact that some media can break up if tumbled with strong water flow, causing bits and pieces of the media to escape the filter or media reactor and get into your aquarium. Sometimes, the media is more effective if it is tumbled quickly and can cause very detrimental affects if the flow is too low. Two prime examples of each of the scenarios above are GFO and biopellet media. If the flow through GFO is too strong, it will tumble and break apart, coating the inside of your sump or aquarium with red flakes. If the flow through biopellet media is too slow, hydrogen sulfide could be produced, which is very harmful to aquarium life.