The Salty Side: Saltwater Aquariums for Beginners

What is Mechanical Filtration Media?

Mechanical filtration media (vs Biological Filtration Media) is what extracts unwanted ammonia, nitrites and other particles and detritus from the water in your aquarium. Water passes through this media filtering it thereby returning clean water back into the tank.

This type of media does encourage the growth of nitrifying bacteria, but it is so efficient at it’s job of removal that it is used by many, if not most reef keepers.

If you’ve ever owned a freshwater aquarium then you will more than likely have been using a mechanical filtration system. The principle is the same with saltwater aquariums however it needs to be closely monitored in order to prevent it becoming what is known as a ‘nitrate factory’.

Ammonia and nitrites soon become too overwhelming for bacteria to break it down fast enough. As nitrates begin to rise the media must be removed and cleaned or binned, depending on what you are using.

Mechanical Filtration Examples


  • Filter Socks
  • Course and Fine Sponge
  • Filter Floss

Filter Socks

Filter socks are widely used as the primary mechanical media/filtration. They are secured to the sump inlet to ensure that all display water passes through them before continuing into the sump itself.

Depending on your system, filter socks can become blocked with waste fairly quickly and need to be removed and washed often.

Mechanical Filtration Media

Leaving any dirty or unwashed mechanical filter media in the sump will not only cause the water to pass over the top of them (making them ineffective), but also encourage nitrates to rise.

Filter socks can be difficult to clean. See here to find out how to clean filter socks.

Course and Fine Sponge

Sponge can be used as a secondary method of mechanical filtration in a sump, possibly between baffles, or as primary mechanical filtration in a salt water tank with rear compartments.

Theoretically, the water should pass through the courser sponge first, then through the finer sponge. This will prevent larger particles clogging up the finer sponge too quickly.

Sponge must be closely monitored for detritus build up, and must be washed often to ensure it is always effective.

Sponge can be washed in water change water, or mixed salt water to help retain any bacteria that may be in residence.

Filter Floss

Filter floss is well known for its ability to ‘polish’ the water running through it as it traps even the smallest of particles. But, it is also just as well known for its potential to cause nitrate problems if not used correctly.

Generally speaking, filter floss needs to be changed every 2-4 days depending on the system. This will ensure that it does not become detrimental to your aquarium.

Filter floss is on the edge of acceptance in marine systems. Not very many aquarists use it for constant filtration because of its potential for exacerbating nitrate levels. It is however, often used when the water needs to be cleared quickly after a water change, or when a rockscape has been moved.

Personally, I don’t use it. I rely solely on filter socks as the primary method of mechanical filtration of water in my reef tank.


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