Hi, I have a Fluval 405 and I was just wondering, how often you should change the bio rings? I was told never to clean them completely as they contain very important bio for my health of my fish. Lately, my take was very cloudy, probably from my over feeding and over crowding my tank. However, in the last 9 yrs. I have kept the same bio rings in and cleaned them fairly good. Yesterday, I actually got rid of them and put in new rings...Today, my tank is crystal clear!!! also, very amonia free....