When it comes to aquarium filtration ‘most’ people believe they know what is meant by an aquarium filter. I would like to think that by and large most people understand the nitrogen cycle and thus understand what a filter needs to perform and to keep your tank inhabitants healthy.

Many people however still do not understand that filters often have 3 main components.

Biological filtration, chemical filtration and mechanical filtration.

Today we are going to take a look at these 3 main types of filtration and what each type of filtration performs in your aquarium.

Each filtration type is made up of differing media designed to perform their own unique tasks within your aquarium. It does not matter whether these forms of filtration are contained within in tank filters, canister filters or sumped systems as they perform the same duty irrespective of location.

Mechanical filtration is usually the first stage of any filter. This form of filtration should not alter the chemical makeup of your water or interfere with the parameters in any way. Mechanical filtration simply removes particles, food, waste and debris from the water column thus aiding further steps of filtration (i.e. biological). This can be in many forms. Filter floss or filter wool, sponges of varying coarseness, filter socks or even the newer roller mat technology. All will aid mechanical filtration in various ways or degrees, some more effective than others.

It is important to change the mechanical filtration regularly as any build-up of the waste, food and debris that is caught within it will cause it to compose and negatively affect water quality.

Mechanical filtration such as filter socks and roller mats are often graded in microns. The smaller the number the finer the material meaning more debris and waste will be caught, but that also meaning the material will become ‘used’ quicker. The larger the number the more freely debris and waste will pass through it, also meaning it will last longer. Some people prefer to use a throw away replaceable material while others prefer to reuse and wash filter socks or similar. There is no right or wrong answer and everyone has their own preference. Various methods have differing pros and cons that can be considered by the hobbyist.

Usually the second stage of any filter, albeit the order isn’t crucial is biological filtration. Biological media is anything inert that can provide a surface area for aerobic bacteria to break down waste as part of the nitrogen cycle.

Our reef tank inhabitants produce waste and bio load in the form of ammonia a substance toxic to fish. The aerobic bacteria then colonise within our biological media in an oxygenated environment which then consumes this ammonia, this bacteria within the biological filtration then reproduces rapidly until the ammonia is all gone.

As these bacteria consume the ammonia they give off nitrite, another product toxic to our fish. Another bacteria will then consume the nitrite for energy albeit at a slower rate than the initial bacteria that converted it from ammonia.

Lastly the nitrite is converted into nitrate which is less toxic. It must be said that while nitrate is less toxic to our aquatic life it is just that LESS. It is not non-toxic and shouldn’t be left to build up. Nitrate can be removed via water changes or nutrient export methods like algae beds, scrubbers or nitrate reactors.

In order for this waste in its initial form of ammonia to be converted from its toxic form and into nitrate where it is less toxic an adequate biological filter is required. Materials such as Siporax, K1, Marine Pure, Biohome, bio balls and live rock all provide this bacterial home allowing this to happen. Some materials claim to be more porous and therefore more effective with some even being so porous that in certain conditions they harbour anaerobic bacteria that can convert nitrate to nitrogen.

It is important to protect the biologicals media so it does not become blocked or clogged and prevent the bacteria from working. This is why we use a mechanical filter first, i.e. floss or filter socks.

Many older methods of reef keeping relied upon good strong flow and live rock to achieve this but more modern methods of reef keeping have seen us scaping tanks with less rock in a minimalistic way and utilising some of the previously mentioned medias in our sumps or canisters to achieve this nitrogen cycle.

It is important that when clearing debris or particles caught within your biological filtration care is taken not to kill the bacteria that has colonised within it. Sometimes excess food or waste can accumulation and the need to ‘clean this type of media arises. Ensuring you thoroughly shake in old tank water as opposed to cleaning under fresh water will ensure this bacteria is not killed off. Imagine it much like you would with a fish, rinsing that under fresh Salt or RO may likely shock or kill it and the bacteria is much the same.

Where there is a requirement to repopulate a biological filter in a quick time frame ready to host life or to repopulate an existing but diminished or cleaned biological filter, products like ATM Colony, Fritz Turbostart & Dr Tims one and only could be used. These same products could be used at the start of the medias life to kick start the cycle (when following their respective instructions) and avoid the need to wait extended periods of time before fish stocking.

Again, there is no right or wrong answer on what product you may choose to use, many have pros and cons and ultimately the choice is of the hobbyist.

Lastly the final stage of filtration for many people is chemical filtration. Chemical medias are often used to remove unwanted things like organics, harmful elements, medicines and toxins from our aquariums. Chemical media is not essential for reef keeping albeit likely used by most hobbyists.

The removal of excess nutrients like phosphates will often see hobbyists use chemical media like Rowaphos, Nyos PhosiEx, Phosguard and a whole host of other names to remove them. Some people will prefer to adopt a more natural approach with methods like algae beds but another proportion will prefer to fluidise these chemical medias or utilise them in mesh bags to absorb the excess nutrients instead.

Carbon is probably the most popular of all chemical medias used in tanks worldwide. Activated carbon is often used for a host of reasons; to remove organic materials from the water, to remove harmful elements such as copper and chlorine and also absorbs many medications. It’s important therefore if treating tanks for disease or illness that you remove this type of filtration before doing so and only add it at the end to reabsorb those elements.

As carbon becomes ‘spent’ its pores become full and it will need to be replaced with fresh media. Its use will make your aquarium water look clear by removing the organics and decolourants and it is a popular addition to most aquarium filters.

Additionally, some chemical medias can come in liquid form requiring to be ‘dosed’ manually or automatically to our aquariums. Some agents used to bind and non-toxify ammonia, phosphate removers and things such as water clarifiers often come in this liquid form.

Any of these filtration types can be added to existing aquariums as well as used in the setup of new ones and consideration of all 3 types will ultimately put you on the right road to success in your reef aquarium.

As a lifelong adult hobbyist, making it almost 15 years in the making, Danny has been keeping Saltwater for quite some time. As one of the biggest passions in his life in 2014 he combined that with his second biggest passion, photography and videography.