here is a great post that everybody can use.
Different types include undergravel (UGF), internal, and external. The external category can further be broken down by hang-on-back and canister. There is also an additional type of external filter called wet-dry or trickle filters.
There are also different tasks that are accomplished by different types of filtration. These include biological, mechanical, and chemical. Biological filtration is also refered to as bacterial cycling, where ammonia is oxidized into nitrItes and then further oxidized to yield nitrAtes. Mechanical filtration, as the name implies, is simply straining particulate material from the water. Chemical filtration makes use of acivation carbon, zeolite, peat, or synthetic resins to chemically alter the water composition.
With that out of the way, let's look at the basic filter types along with the pros and cons of each:
(1) Undergravel Filter (UGF) - This used to be the filter of choice when I started fishkeeping, but has fallen out of favor in the past decade or so. It is comprised of a perforated plate that rests on the aquarium bottom. A layer of gravel is placed on top and powerheads or airlifts are used to draw water down through the gravel and up through the uplift tubes and out to the aquarium. Fish wastes and excess food are drawn down into the bacteria-rich substrate where it is converted it to nitrItes, then nitrAtes. Works primarilly as a biological filter, but also serves as some mechanical filtration as the solids are drawn towards the substrate.
Pro: Simple to set up and operate.
Con: Tend to clog up with detritus. Excessive build-up of organics believed to be major contributor of "old tank syndrome" or otherwise unexplainable crashes. Not plant-friendly. Little or no chemical filtration options. Can create oxygen deprived conditions.
(2) Internal Filter - These are typically small boxes that are placed in the aquarium and utilize either an airlift (old-style - I'm not sure these are made any more) or small internal pump to draw water through the filter media. The media is usually comprised of a sponge for mechanical/biological filtration and there are often provisions for additional chemical media.
Pro: Inexpensive. Effective. Versatile. Often the filter of choice for raising or growing out fry.
Con: Often unattractive. Maintenance requires disturbing aquarium and its inhabitants.
(3a) External Hang-On-Back (HOB) Filter - These are probably the most popular filters for small to moderate sized tanks (75 gallon and less). Water in drawn through a siphon tube by a small self-contained pump and expelled through the filter media and then returned to the tank. The choices of filter media are almost limitless and include sponge for mechanical/biological filtration; activated carbon, peat, zeolite (ammo-chips), phosphate absorbing resins, and others for chemical filtration/treatment as desired. In addition, some filters such as the Marineland Penguin and Emeror models also include bio-wheels that add substantial bacteria colonizing potential in an oxygen-rich environment that is optimum for their well-being.
Pro: Relatively inexpensive (great bang for the buck). Extremely versatile. Easy maintenance. In addition, I have found HOB filters from reputable manufacturers to be very durable (I have a Hagen AquaClear 500 that is several years old and has been trouble-free).
Con: Sometimes noisy, although this is usually a waterfall noise that can often be remedied by topping off the aquarium. Require adequate space behind aquarium.
(3b) External Cannister Filter - Cannister filters pump water through an inlet tube, pass it through the selected media, and then return it to the tank by way of an outlet tube. These offer the same versatility as their HOB brethren. They are often employed in larger tanks (55 gallon and larger) and are usually housed in the stand.
Pro: Extremely versatile. Usually virtually silent operation. Design allows for selective placement of inlet and outlet tubes. Usually very durable. Fairly easy to maintain. Require very little clearance behind tank. Can be placed out-of-sight.
Con: Expensive. Tend to foul fairly quickly in cases of power outages.
(4) Wet-Dry or Trickle Filter - Water is drawn from the aquarium by an overflow box or similar arrangement and then trickles through a tower that contains plastic or ceramic media that encourages bacterial growth. The water then collects in a sump and is then pumped back to the aquarium. Chemical filtration media can be placed in the sump as desired. These are almost exclusively reserved for big tanks (in excess of 100 gallons).
Pro: Very efficient biological filtration. Versatile.
Con: Very expensive. Often noisy from the overflow box, the trickle tower, and/or the return pump. Complex and often problematic.
Different types include undergravel (UGF), internal, and external. The external category can further be broken down by hang-on-back and canister. There is also an additional type of external filter called wet-dry or trickle filters.
There are also different tasks that are accomplished by different types of filtration. These include biological, mechanical, and chemical. Biological filtration is also refered to as bacterial cycling, where ammonia is oxidized into nitrItes and then further oxidized to yield nitrAtes. Mechanical filtration, as the name implies, is simply straining particulate material from the water. Chemical filtration makes use of acivation carbon, zeolite, peat, or synthetic resins to chemically alter the water composition.
With that out of the way, let's look at the basic filter types along with the pros and cons of each:
(1) Undergravel Filter (UGF) - This used to be the filter of choice when I started fishkeeping, but has fallen out of favor in the past decade or so. It is comprised of a perforated plate that rests on the aquarium bottom. A layer of gravel is placed on top and powerheads or airlifts are used to draw water down through the gravel and up through the uplift tubes and out to the aquarium. Fish wastes and excess food are drawn down into the bacteria-rich substrate where it is converted it to nitrItes, then nitrAtes. Works primarilly as a biological filter, but also serves as some mechanical filtration as the solids are drawn towards the substrate.
Pro: Simple to set up and operate.
Con: Tend to clog up with detritus. Excessive build-up of organics believed to be major contributor of "old tank syndrome" or otherwise unexplainable crashes. Not plant-friendly. Little or no chemical filtration options. Can create oxygen deprived conditions.
(2) Internal Filter - These are typically small boxes that are placed in the aquarium and utilize either an airlift (old-style - I'm not sure these are made any more) or small internal pump to draw water through the filter media. The media is usually comprised of a sponge for mechanical/biological filtration and there are often provisions for additional chemical media.
Pro: Inexpensive. Effective. Versatile. Often the filter of choice for raising or growing out fry.
Con: Often unattractive. Maintenance requires disturbing aquarium and its inhabitants.
(3a) External Hang-On-Back (HOB) Filter - These are probably the most popular filters for small to moderate sized tanks (75 gallon and less). Water in drawn through a siphon tube by a small self-contained pump and expelled through the filter media and then returned to the tank. The choices of filter media are almost limitless and include sponge for mechanical/biological filtration; activated carbon, peat, zeolite (ammo-chips), phosphate absorbing resins, and others for chemical filtration/treatment as desired. In addition, some filters such as the Marineland Penguin and Emeror models also include bio-wheels that add substantial bacteria colonizing potential in an oxygen-rich environment that is optimum for their well-being.
Pro: Relatively inexpensive (great bang for the buck). Extremely versatile. Easy maintenance. In addition, I have found HOB filters from reputable manufacturers to be very durable (I have a Hagen AquaClear 500 that is several years old and has been trouble-free).
Con: Sometimes noisy, although this is usually a waterfall noise that can often be remedied by topping off the aquarium. Require adequate space behind aquarium.
(3b) External Cannister Filter - Cannister filters pump water through an inlet tube, pass it through the selected media, and then return it to the tank by way of an outlet tube. These offer the same versatility as their HOB brethren. They are often employed in larger tanks (55 gallon and larger) and are usually housed in the stand.
Pro: Extremely versatile. Usually virtually silent operation. Design allows for selective placement of inlet and outlet tubes. Usually very durable. Fairly easy to maintain. Require very little clearance behind tank. Can be placed out-of-sight.
Con: Expensive. Tend to foul fairly quickly in cases of power outages.
(4) Wet-Dry or Trickle Filter - Water is drawn from the aquarium by an overflow box or similar arrangement and then trickles through a tower that contains plastic or ceramic media that encourages bacterial growth. The water then collects in a sump and is then pumped back to the aquarium. Chemical filtration media can be placed in the sump as desired. These are almost exclusively reserved for big tanks (in excess of 100 gallons).
Pro: Very efficient biological filtration. Versatile.
Con: Very expensive. Often noisy from the overflow box, the trickle tower, and/or the return pump. Complex and often problematic.