Filtration and filters


Filtration is a vital part to an aquarium. Aquaria are heavily stocked compared to in nature, and so the water becomes polluted rapidly with excreta and other organic matter.

There are 3 types of filtration:

  • Mechanical
  • Biological
  • Chemical

Mechanical filtration

Mechanical filtration removes particles to give clear water.

This is achieved simply by including a fine medium to the filter, literally acting as a sieve. Naturally, the finer the sieve, the more easily and quickly the filter becomes clogged and requires cleaning. A compromise is therefore met, between how efficient the sieve is and how often it must be cleaned.

Biological filtration

Biological filtration converts ammonia, which is toxic to shrimp, to less harmful nitrites, and nitrites to less harmful nitrates. (See ‘nitrogen cycle’)

This is achieved by providing a surface for nitrifying bacteria to colonise with a constant flow of water passing through it. As the water does so, the bacteria convert the ammonia/ammonium in the water into nitrites, and the nitrites into nitrates. These nitrates leave the water by water changes or uptake by plants and algae.

Chemical filtration

Chemical filtration removes compounds and ions that are directly or indirectly harmful from the water. (These species are removed with water changes also)

This is achieved by adding reactive media to the filter. The most common media is activated carbon, which adsorbs many organic compounds, and chlorine and chloramines present in tap water. With time the activated carbon will become exhausted and will need replacing.

It is my opinion that, in shrimp aquaria, only biological filtration is necessary. Mechanical filtration should not be necessary as there should be little or no debris present in a shrimp aquarium. Water changes should be frequent in shrimp aquaria due to how sensitive they are, and so chemical filtration is also unnecessary.

Having said that, it is a good back-up to have chemical filtration media handy. I personally always have activated carbon ready for use in case any contaminants enter my aquaria and begin to harm the shrimp. I have had good results with using bamboo charcoal shelters for shrimp also, which can be purchased online (aquatics shops and eBay).


There are many methods of filtration available for aquaria. The sheer number can be overwhelming. This guide of filter types will hopefully help the aquarist interested in shrimp to make an informed decision on which filter is best for them.

Under-gravel filter

The under-gravel filter is a very old design. Panels are placed at the base of the aquarium with a funnel connected to one, and a substrate is applied on top. An air stone is placed at the bottom of the funnel and connected by tubing to an air pump. When the air pump is turned on, air bubbles up the funnel and creates a flow through the substrate and panels, and up the funnel. Alternatively, a powerhead is connected to the top of the funnel.

Mechanical filtration – This depends on how fine the substrate is. The finer the substrate, the greater the mechanical filtration. This is because with large grain substrate the particles in the water easily pass through, whereas with smaller grain the particles are more likely to be held in the substrate. This can be problematic, however. Particles can lead to clogging of the substrate, restricting further filtration. Finer substrates can also become compacted over time and also clog the filter. Make sure the substrate grains are large enough to prevent being pulled through the panel slits!

Biological filtration – The nitrifying bacteria occupies the surface of the substrate grains, so finer substrates give more efficient biological filtration as it provides a larger surface area. Under-gravel filters give a very large surface area and are efficient at this type of filtration. With fish, under-gravel filters can become clogged with excreta, but this doesn’t tend to be a problem with shrimp due to their low bioload.

Chemical filtration – Under-gravel filters typically lack this type of filtration. However, they can be adapted by putting layers of chemical filtration media in the substrate (such as zeolite and activated carbon). They can not be removed or replaced once applied.

Further notes – This filter type can not be removed or cleaned in aquaria. Some breeders connect the funnel of the under-gravel filter to the outlet pipe of external filters to create a reverse under-gravel filter system. This helps to prevent the substrate clogging.

My opinion It is in my opinion than under-gravel filters are very useful, but should not be relied upon on their own. They are particularly useful for getting the full use out of active soils that alter water chemistry by ensuring a good flow of water throughout the substrate.

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