In the high-tech world of reef-keeping, mechanical filtration doesn’t seem that exciting. Compared to protein skimmers, media reactors, and denitrifiers, mechanical filtration is probably an afterthought for many reef aquarists.

The truth is, there is a lot of stuff floating around your reef tank that can have a major impact on its health. Here’s what you need to know about particulate matter, how it affects the aquarium, and how to remove it with mechanical filtration!

Let’s start by identifying the types of particulate matter that build up in a reef tank. To keep things simple, we’ll break it down into three types: Living, Dead, and Mineral.

Aquarium water is teaming with life. Despite water looking clear, its filled to the brim with microscopic algae, bacteria, and crustaceans. These tiny life forms make up the vast majority of life in our tanks.

Plankton is are constantly dying off in your aquarium. As the tiny creatures reach the end of their life cycle, they will begin to break down and release organic waste into your system. This waste is also contributed to by waste from your larger livestock and leftover food.

Over time it is pretty common to see a build up of whitish sediment on the bottom of your tank. This tends to be a combination of numerous particulates including crumbling live rock, shell fragments, carbonate scraped from the aquarium glass, and bits of encrusting algae.

These are the three most common types of particles you will find in a reef tank. But as always, there’s more, check this out. Similar to how dust settles on surfaces, aquarium debris will settle on coral. Once this dust builds up enough, the coral will release a slime. The slime grabs the particulates and is released into the water column, leaving the clean and happy coral behind.

As the slime passes through the water it continues collecting free floating debris. If it collects enough, it will become very easy to see and can make it look like someone sneezed in your tank.

In nature these particles will sink to the bottom of the ocean as “marine snow”. Unfortunately our tanks aren’t quite as deep as the ocean so it settles on the bottom in a rather unsightly manner if not removed. This is why mechanical filtration is so important.

In a system where there is no mechanical filtration, floating particulate will often get trapped in chemical filtration media such as carbon bags and phosphate removers. As it begins to clog the media, it reduces water flow and efficiency. The build up organic waste will also begin to decay and stimulate bacteria growth, coating the media.

In low flow areas such as corners, under rock, and in your sump, suspended debris will often fall out of solution and settle. This build up results in ugly sludge patches in these dead areas. Low flow refugiums are a typical problem spot of this build up as well. Unfortunately this means your fuge can turn into a junk yard instead of a gentle refuge.

Flow pumps and powerheads are your best friend when it comes to stopping debris from settling; however, without mechanical filtration you will just be pushing abrasive sediment through your delicate equipment rather than removing it. Overtime this sediment can grind away at impeller shafts and bearing, massively reducing their efficiency and lifespan.

The more corals you have, the more potential slime you are looking at. If not filtered, the slime will carry debris into your protein skimmer and effect its ability to efficiently produce foam and remove organics. This is why it’s best to put your mechanical filtration in before your skim.

Both floating particles and organic slime can affect light in your tank as well. As light passes through the water column, it hits everything that is in your water. The more particulate there is in the water column, the more the light bounces and scatters, reducing how much light actually makes it to your corals.

One of the most standard types of mechanical filtration is a filter sock. Pretty much all sumps now days come with a built in sock holder and even those that don’t can easily be retrofit with one. Filter socks were originally employed for industrial air and liquid filtration, but they have since been scaled down and become a mainstay in our hobby.

The typical way that filter socks is rated is by their micron count, the most common of which are 200 and 100 microns. Just remember, the smaller the micron, the smaller the holes.

When you install a brand new 200 micron sock, it will only really filter out particles that are 200 microns or larger. Over time, the filter pores will begin to clog and remove continually smaller and smaller debris. As the pores become more and more clogged water will begin to backup and the socks water level will begin to rise. This is the point when the sock either needs to be cleaned or replaced.