What is Saltwater Aquarium Filtration

Most saltwater aquarium systems require external filtration. The primary purpose of filtering your aquarium’s water is to remove organic waste created in the system. While this is an essential part of maintaining an aquarium, many beginners are overwhelmed with the plethora of filtration choices available. This article explains the basics—only what you need to know to get started. Additional research will be necessary to decide what is best for your specific system.

Think of your saltwater system’s filtration as a point-of-use Brita filter installed on your kitchen sink. The overflow from your display tank is like the kitchen faucet which channels water into the filter housing or, in the case of your saltwater system, the sump (little more than an acrylic box resembling a fish tank or even an inexpensive plastic tub). In the same way that “cleaner” water comes out of your point-of-use filter mounted on the kitchen faucet, the water coming out of your sump is also of a higher quality if you have set the sump up properly.

The process is not magic. In the case of your point-of-use filter on the kitchen faucet, the water, once it enters the filter housing, moves through a multi-tiered filtration system. In this system, activated carbon, ion exchange resin and other filter media remove impurities, heavy metals and particulate matter from the tap water through both mechanical and chemical filtration. These impurities are then removed from the system altogether by cleaning or replacing the filter cartridge.

The aquarist also relies on mechanical and chemical filtration to improve water quality (most aquarists also rely on biological filtration, but that’s another article). The water entering the sump from the overflow is often run through a filter sock which effectively filters out the larger particulate waste. Next, in the simplest set-up, the water moves from the first chamber of the sump to a second chamber and, in the process, passes through one or more types of filter media. This filter media, at its most basic level, is simply a filter pad designed to trap particulate matter. Once the water has flowed into the second chamber of the sump, it is then pumped back to the display tank. In addition to a filter pad, a filter bag can be filled with a wide range of filter media (such as activated carbon) to address various water quality issues. Like the Brita filter, the waste is then permanently removed from the system by cleaning or replacing the filter media.

While the above set-up will improve water quality, most marine aquarists also rely on a protein skimmer. The protein skimmer is usually placed into the first chamber of the sump where it skims the water entering from the overflow (skimmers require their own dedicated pump to operate). Protein skimming removes dissolved organic nutrients from the water before those nutrients are broken down by bacteria. Because a protein skimmer removes organic nutrients, it is possible to overskim your system. As a result it is important to properly install, run and maintain your skimmer according to the manufacturer’s directions.

While there are many other possible configurations, this article has focused on the basic system. In the configuration described above, the system water continually exits the display tank through the overflow, is filtered through a filtration sock, skimmed by a protein skimmer, filtered again through a filter pad and/or a filter bag filled with appropriate filter media (such as activated carbon) and then finally pumped back to the display tank.

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