The efficiency of a biological filtration system of a saltwater aquarium depends of three factors: the surface area of the biological filter media upon which nitrifying bacteria can grow, the speed with which the material to be processed (ammonia, nitrites and nitrates) are passed by the bacteria and the quantity of bacteria on the surface area. Choosing The Right Biological Filter Material can go a long ways in improving any filtration system.
The first biological filtration consisted of whatever nitrosoma bacteria exists on the surfaces and in the water in the tank. One of the first constructed filters for aquariums was the Under Gravel Filter (UGF) which was fairly simple to build as a DIY project. The UGF filters did have the drawbacks of generating a lot of nitrates from decaying detritus and other material trapped under the filter plate as well as requiring a lot of maintenance. The Under Gravel Filter Controversy was a result of these problems. Still, though, UGF's do serve a purpose for certain applications.
The next filters in line to be popular were the Live Rock (often called the “Berlin Filter Method") and the Wet/Dry Trickle Filter. The Berlin Method consisted of using the surface of Live Rock as a platform for the nitrifying bacteria (nitrosoma and nitrobacter) which convert the ammonia produced in your tank into nitrites and then nitrates.
A basic wet/dry trickle filter consists of vertically passing filtered aquarium water over an exposed filter media, then into a receptacle, usually a sump. As the water passes over the filter media, the ammonia and nitrites in the water are processed by the resident nitrobacter and nitrosomona bacteria into nitrates. As the water passes over the filter media, it is exposed to air, allowing the free exchange of gasses (O2 & CO2). The rapid oxidation of ammonia and nitrite makes these filters extremely efficient; they are an outstanding choice for freshwater and saltwater aquariums.
Power Filters (also called “Hang On Tank Filters) became popular due to their ease of use. The first ones on the market were not all that efficient as either a mechanical or biological filter, but later models utilized improvements such as larger sizes, a bio wheels and more efficient pumps to improve performance.
Canister Filters were the next in line to become popular. Used for mechanical, chemical, and/or biological filtration in saltwater aquarium systems, canister filters are quite versatile. A canister filter can be used continuously, or added and run only when needed. They can act as a stand alone filter, or be used in combination with other types of filtration as well. As more manufacturers entered the canister filter market, the filters became bigger, more efficient and easier to maintain.
As you can see in the Top Canister Filter Picks, there are well over a dozen aquarium canister filters on the market today. There are even nano aquarium canister filters for the smallest of aquariums.
To aid increased biological filtration in an aquarium, a number of Nitrifying Bacteria Tank Starters are on the market which assist the cycling process in a tank. Some contain a quantity of the nitrosoma and nitrobacter bacteria which can help cycle your tank faster (some as fast as 1 day) than normal. Others contain enzymes which help naturally occurring bacteria grow more rapidly. Some products are added only at set up, others need to be replenished periodically.
As you can see, vast improvements have been made in aquarium filtration systems to greatly increase their biological filtration efficiency and aid the modern aquarist.