Aquarium Filters

All fish produce waste and within a close system (an aquarium) this waste needs to dealt with otherwise they can reach toxic levels. In basic terms aquarium  filters break down the waste materials in the water and make them ‘safe’. At least 90% of health problems are down to water quality, healthy water equals healthy fish. Healthy fish often carry disease and it is when poor water quality reduces their immune system efficiency that these diseases take hold. There are 4 types of filtration: Mechanical, chemical, sterilization and biological. Each type is normally used alongside another to meet the needs of the system.

Mechanical Filtration

Normally the first stage of the filtration process and is the removal of solid waste. Within an aquarium this is normally by a coarse foam/ sponge material.

Biological Filtration

Is the most essential part of the filtration process. Nitrogenous pollutants are removed or converted by beneficial bacteria. Ammonia created by the fish is broken down to Nitrite and then more bacteria break Nitrite down to Nitrate. Nitrates are then normally removed via water changes or up taken by plants and algae. Basic internal filters only have a single sponge which is both Mechanical and Biological. Care must be taken during maintenance to ensure that these bacteria are not killed off. Never wash these sponges under the tap, use aquarium water which has just been removed. Both ammonia and nitrite are toxic to fish and a mature healthy aquarium should not have a reading of either.

Filter bacteria takeRecommended Filtration time to develop in numbers and only build up in proportion to the amount of ‘food’ (fish waste) available. There are many treatments available on the market which help to speed up this process. Even with these treatments we advise adding fish slowly to the aquarium and waiting a week before the first ones are introduced and start with the hardier fish. Click on this link to see a list of recommended filtration available on Amazon. 


Chemical Filtration

This normally comes in the form of carbon or another material like Purigen. These materials are either placed in a media bag or in a reactor within the filter system. These materials 'suck out' certain impurities from the water. In the case of carbon it removes discoloration and reduces odors. With PurigePurigen Link available on Amazonn® this product controls ammonia, nitrites and nitrates by removing nitrogenous organic waste that would otherwise release these harmful compounds. Click on this link for a list of recommended filter media which is available on Amazon.


Water is passed by an Ultra Violet bulb which emits a lethal wave length of light killing off algae and pathogens. They have a special UVC bulb which if looked at directly can damage eyes so they are well sealed within the unit. Please follow the manufacturers advice and instructions when installing and maintaining these items of kit. In pond they are also useful for clearing green water but within an aquarium they are used for disease control.


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