Saltwater Aquarium Filtration

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What Filtration System Should I Use?

Now that you have decided on a particular system it's time to select the proper filters for that system. Firstly, every tank system needs a biological filtration system; this is the foundation filter that all other filters will be based around. Without this type of filtration your tank can go bad fairly quickly. Good water quality is essential for a healthy ecosystem. Bacteria, algae and impurities thrive in poor water conditions making your tank inhabitants susceptible to illness and death. Invertebrates, in particular, will be the first to show the effects of poor quality water.


Filtration should be adequate enough to keep ammonia and nitrate levels below detectable levels. Adequate water movement should be maintained and provide for good gas exchange. Good water movement and surface aeration are essential in a filtration system, especially to help ensure that the oxygen in the water is dissolved correctly. Warmer water temperatures sometimes prevent this from happening, which can suffocate the fish.

Water movement (current) is crucial to the long-term health of your aquarium. Currents help feed and nourish inhabitants, wash away waste products and sediment that promote damaging algae growth, and help fish burn off excess fat found in many commercial fish foods.

There are three types of filtration that you should be aware of:

1. Biological Filtration (nitrifying bacteria)A biological filter is a living entity that takes in oxygen and unwanted substances from the water. It generates its own waste products and creates a setting for beneficial bacteria to breed. Toxic ammonia from the waste is turned into Nitrite, which is then turned into Nitrate. Algae growth is encouraged by the presence of nitrite. Biological filtration uses live rock and bacteria to process waste. Biological filtration is the process in which beneficial bacteria convert organics that have been broken down into the toxic elements of Ammonia and Nitrite into the less harmful compound Nitrate, which can then be removed by water changes or chemical means. The process of Biological filtration does not happen fast and usually takes between four to six weeks to be established.

2. Mechanical Filtration (floss media, paper cartridges and sponges)A mechanical filtration system separates un-dissolved waste from the water but will not eliminate dissolved waste, bacteria, algae or debris. This is simply the removal of suspended particles of waste, excess food, plant matter and general dirt from the aquarium. Most filters employ some sort of mechanical filtration through filter floss, pads or sponges that trap the waste as water passes through it. Water is pushed through a strainer (filter media) which catches all free-floating particles unable to pass through the filter. Filter media includes filter floss, filter pads, gravel, and a sponge. This type of filtration system is basically used in fresh water tanks and not recommended for saltwater or reef tanks.

3. Chemical Filtration (gas activated charcoal)Chemical filtration systems eliminate liquefied impurities from the water. Carbon or chemical resins aggressively work to extract toxins from the water until the filter is saturated. This type of filtration system therefore needs to be changed often.

To achieve the desired results, the different types of filtration above should be used alone or in combination. This is achieved through the use of various media or resins placed in the filter. These media removes dissolved waste materials such as fish waste, etc. that can cause odors and discoloration of the aquarium water. Chemical media placed inside the filter can also remove Phosphates, Nitrates, Ammonia and many other toxins. The most common form of Chemical filtration is the use of activated carbon. Again, this type of filtration is for freshwater tanks and not recommended for saltwater or reefs tanks.

Additionally other types of filtration systems should be considered. Some of the filters below are often used.

  • Protein Skimmer

Also referred to as "foam fractionators" or "absorptive foam separators." Works by removing organic compounds from the water by means of air bubbles that bring waste to the tank surface. The foam that is produced is then deposited into an enclosed compartment. This type of filtration is mainly utilized in reef tanks. It eliminates liquefied impurities prior to them decomposing. Each type of skimmer has its own good and bad points, but the bottom line is that you have to know where you are going to put the skimmer. In tank skimmers are the least expensive but offer the fewest options. The in sump models offer the most features, but are among the most expensive. The models that hang on the side of the tank are by far the most popular due to their reasonable prices and easy installation.

  • Canister Filter

This is a multipurpose filter that may be used in conjunction with supplementary filtration equipment or could be the sole filtration device. Water is forced through filter media to trap debris. It can be placed inside or outside the tank.

It should be considered if you plan on having a lot of fish in the tank because it is the most ideal and most powerful filter system for this purpose. The downside is that it requires frequent cleaning since bacteria settle in it. These types of filters can be used in a saltwater or reef tank but work best in a freshwater tank.

  • Wet/ Dry (Trickle Filter)

A Wet/Dry Trickle Filter requires oxygen to function to accommodate the good bacteria. However, mechanical filtration is not needed. It utilizes organic filter media such as bioballs or floss located within the filter itself. Water trickles over the media and creates a large air-to-water surface attracting debris to the structure of the media.


Wet/Dry Trickle filters may include a sump pump for custom filtration. The additional space provided by the sump allows plenty of room to install a variety of advanced filtration systems including protein skimmers. This dramatically improves water conditions.

Pros and cons of using these filters:

Wet/dry trickle filters have been a popular choice in biological filtration for a very long time in the saltwater hobby. However, as the technology in aquarium keeping has advanced and the desire to attain a "natural" reef system becomes ever popular, controversy surrounds this choice.

Often referred to as nitrate factories, many aquarists believe that wet/dry filters are suitable for fish-only tanks, but not reef systems. Over time the bio-material inside the wet/dry chamber becomes dirty, which eventually leads to a build up of unwanted nitrates in the aquarium, and as you should know, nitrates are not reef friendly! Therefore, to better understand this type of biological filter choice, let's take a closer look at how it works and its three basic components; the drip/trickle plate, the pre-filter set up, and the biomaterial used inside.

  • Fluidized Bed Filters

Sand is the main component of this somewhat new type of filter. Elevated water circulation allows sand to remain free of waste. It also doesn't inhibit the growth of beneficial bacteria, however it may become obstructed as well as reduce oxygen level in the tank. The mechanics of this type of filter are simple. It is comprised of a tube filled with sand, which is submerged. Water is pumped through the tube allowing the bacteria to settle. Although it offers a large area for bacteria, it offers poor performance in that it doesn't create an adequate supply of oxygen. Fluidized bed filters are one of the best choices for planted aquariums. The filter will not drive off the valuable CO2, yet it is efficient and very low maintenance. Although the bacterial bed takes longer to establish, once it is set up it does not have to be disturbed when performing maintenance, as other filtration systems must. Relatively new, these filters are very efficient biological filters utilizing sand as the filer medium. The small particles provide a high surface area for the bacterial colonies. Although it takes a bit longer to mature initially, the fluidized bed is an excellent biological filter that can be used in any sized aquarium.

Your filtration system's function is meant to reduce the amount & effects of wastes and to stabilize the water chemistry. Choosing the right filter will ultimately come down to the size of the tank, the type of tank and the livestock that will inhabit it. Check with your local pet store to find out what will work best for the tank that you have in mind. 

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