Canister Filters
Canister Filters (hob filters) Hang on Back or Canister filters are becoming more common these days. I have prouped these two filters together since they are essentially very similar in performance and operation. They use two pipes that hang or clip over the back of the tank and water is pumped through the filter which can be on the back or anywhere away from the tank. Usually installed in a cupboard under the tank, but also wall-mountable. This type of filter contains lots of different types of media, depending on the manufacturer. Usually fairly expandable too, so individual choices of media can be made according to need. The recommendation for this type of filter is that it should be large enough to circulate ten times the volume of water per hour, which means that a 100 gallon tank requires a filter capable of moving 1000 gallons per hour!
Advantages:
Power: These filters tend to be very powerful and move a great deal of water, capable of handling high demands on medium and larger tanks. Some are also adjustable so you control the power it uses. Effectiveness: For diggers and bottom dwellers they are very effective, since they clean large amounts of water very quickly. On most tanks where these filters are fitted, they give crystal-clear water all the time.
Visibility: They are easy to hide away, since it is only the two pipes that enter the tank, and these are easy to disguise.
Current: These units create a really strong current from both ends. The intake needs a good pre-filter fitted to stop the inhabitants being drawn in and the outlet creates a very strong circulation in the tank which is perfect for some fish, but not so good for others.
Dis-advantages:
Cleaning: Can be difficult to clean and some need to be primed before they work. There have also been reports of flooding during the cleaning process, as when installed below the tank water level they can act as a siphon if the valves are not closed properly. Not so prone to clogging as they use lots of media.
Cost: These are very expensive units, and maintenance costs can be high too, depending on the type you buy. The recommendations tend to insist on a much larger unit than you would expect to need.
Noise: They can be quite noisy, the HOB filters especially, but canister filters can be installed away from the tank, this means that they can be put in another room if necessary.
