Rotating Drum Filters
Filtering Your Aquarium Water
(The First Tank Guide)
What Is a Rotating Drum Filter?
A rotating drum filter, sometimes called a paddle wheel filter or a water wheel filter, consists of a cylinder of corrugated, highly porous material which is set to turn like a paddle wheel on an old river boat with only one edge in the water at any time. This provides an oxygen rich filtration environment.
How Does a Rotating Drum Filter Work?
Water is either sprayed over the rotating drum or passed under it, causing the drum to spin.
As the rotating drum spins through the water, the fibrous material of the drum picks up water laden with fish waste in the form of ammonia and nitrite. Once the tank has cycled, nitrifying bacteria living in this material can process the ammonia and nitrite in the water into relatively harmless nitrate. Because the bacteria living in the fibrous material of the rotating drum are exposed to air, they have access to more oxygen than their water dwelling cousins, and can therefore process more nitrite and ammonia, and they can process it faster.
What Maintenance Does a Rotating Drum Filter Require?
Ideally, rotating drum filters require almost no maintenance.
As with many filters there is an associated pump which must be kept in good working order through regular cleaning. This will include keeping the intake on the pump clear, and making sure that the impeller is clean and free-spinning. Many rotating drum filters are mounted as integral components in a power filter, in which case, the power filter will require normal maintenance.
Also, any tubing associated with the rotating drum filter will need to be kept clear of debris and waste to ensure sufficient water flow through the system.
You will also need to monitor your rotating drum filter to make sure that your drum is not spinning fast enough to throw water. The water should smoothly flow past or over or under the rotating drum without any spray or splashing. In addition, you will need to watch your rotating drum filter to make sure it does continue to rotate. Even the smallest bit of grit can stop the drum from turning, dramatically reducing the effectiveness of the rotating drum filter.
What Should I Be Aware of with a Rotating Drum Filter?
Rotating drum filters often stop rotating - because the water level gets too high or too low, because the spray bar or tubing leading to it gets clogged or moved, or because some piece of debris prevents the drum from rotating. If the drum quits rotating, the part of the drum out of the water will dry out, and the Nitrifying bacteria in that part will die. This will reduce the filtration capacity of the filter until the drum is started again and bacteria propagates into the section that had dried out. Unfortunately, when part of the drum is dry and other parts are wet, the drum is off balance, and may not start rotating again freely. At this point, the drum may have to be replaced.
Because the drum is mostly out of the water, the filter will cause a substantial amount of evaporation. This could be potentially harmful to your fish, as topping off the tank increases mineral content and hardness. Make sure to always remove water from the tank before topping it off.
Also, because the drum needs to mount over the back of the tank, you will need to provide an opening in the back of the tank cover. This opening will provide a potential escape route for any jumping fish, amphibians, or crustaceans you are keeping in your aquarium.
As the rotating drum collects debris and bacteria, the small openings in the fabric the drum is constructed of become clogged, and no longer allow water to pass through the filter, but instead just to pass over it or bounce off. This can greatly reduce the usable surface area of the filter, reducing the space available for Nitrifying bacteria, and, in turn, reducing the effectiveness of the filter. As these pores become plugged, you can rapidly eliminate the filtration provided by a rotating drum.