What are the disadvantages? You must use a pre-filter to remove waste and it must be kept clean. Fluidized bed filters should also be used along with a power or mechanical filter with a high flow rate.
Trickle (Wet-Dry) Filters
What are they? This filter is placed outside the aquarium and must be below the tank. Gravity forces the aquarium water to feed into the trickle filter where there is a bacteria bed. The bacteria is created by the use of a biowheel, bioballs or other biological medium. The trickling effect of the water plus the exposure to air creates a large bacteria growth that can support large fish loads.
What happens if I keep a reservoir of water in the filter? The biomedia must be kept out water. The mixture of air and a trickle of water is what creates the bacteria bed.
What are the disadvantages? It should be used in conjunction with a mechanical filter.
As you can see, there are many filters to choose from and it may be difficult to make a choice. My recommendation is to start with a lower priced filter that will do the job for your tank. You can always work your way up to an expensive one. Keep your old filter as a back-up in case you have an emergency or save it for the next tank you set up. Once you are hooked on the hobby, it's hard to stop at one tank!
