Internal Canister Filters:
With the popularity of the newer small-to-nano size aquariums, there has been a resurgence in the internal canister filter. Most internal filter designs share the same basic features. A small submersible magnetic drive pump provides the current, and a larger filter chamber is attached to the intake of the pump. In most cases, there will be a foam filter cartridge to act as the mechanical filter. Some internal filters have a small chamber to place chemical media and others will use a filter cartridge that has CARBON impregnated into the fiber pad. The Internal canisters make a great option for filtration in a bare bottom hospital/quarantine tank or a grow-out aquarium for fry.
Two of the Fluval style internal canisters are offered. The Nano filter is rated for aquariums up to 15 gallons and makes a great filter system for the small, 1-6 gallon mini-aquariums. The filter chamber holds a coarse BioFoam to provide surface area for the beneficial nitrifying bacteria and a fine foam portion to act as the mechanical filter. Both can be easily cleaned by squeezing them in water from the aquarium and should not need replacement for many months. The pump has an adjustable flow output and uses a short spray bar to provide a gentle stream of water flow. This allows the filter to be used with smaller fish and shrimp that would be bothered by high current.
The second style is the Fluval U Internal filter. Available in four different sizes for aquariums up to 65 gallons, the Fluval U filter is one of the most versatile internal canister on the market. While the Model U1 has a single foam pad filter, the Models U2, U3, and U4 all offer true three stage filtration, with a foam mechanical pad, a poly/carbon chemical media and Bio-Max rings. The outlet can be configured three different ways, a top outlet to help oxygenate the water, a bottom outlet create turnover of the water column and a spray bar for more gentle uses.
For a straight forward, simple design, Penn Plax offers the Cascade Internal filter in several sizes. These two stage mech/chem filters have an adjustable/directional flow output and an optional spray bar when needed. While the Bio-Sponge should last for many months, the Carbon Cartridge should be replaced every 4-8 weeks. Like most internal canisters, the Cascade can be place either vertically or horizontally in the aquarium. Its slim design makes it a great choice for low water level tanks for turtles and amphibians.
A much more specialized type of internal canister would be one of the AquaTop’s Submersible UV Sterilizer w/ Pump systems. Primarily designed as a submersible UV, the canister does have a mechanical filter to help the UV clarify the water. The UV portion can control free floating algae and most bacterial pathogens. While this canister could be used 24/7, most people only use as needed, running it for several days to clarify the water and then storing it until it is needed again.