Your filter is the most important piece of equipment in your aquarium, it is the life support system for your fish, processing their toxic waste products, removing chemicals, and if used correctly, oxygenating your water.
To work properly, a stable population of bacteria needs to set up home and thrive inside your filter, and incorrect maintenance can prevent this from happening, resulting in all sorts of problems for your fish. Unfortunately, with so many makes and styles of filter, and with a lack of clear, concise instructions (except for the purposes of making sure you buy a specific companies products) it is important you find out yourself how to correctly and economically manage your filter.
How often to clean your filter
Each filter is different and whilst some may need weekly maintenance, others can be left for more than a month or two without any significant problems. The only way to know is through a bit of trial and error to see how much waste matter builds up over a period of time.
In general, internal filters will need cleaning at least every couple of weeks, whilst externals can be cleaned anywhere from two weeks for particularly mucky tanks, to every two months for low waste producing tanks.
Keeping a close eye on the filters flow rate, and when it begins to slow, can be a good indicator of when your filter needs a clean.
Cleaning will damage your filter!
Cleaning your filter can be quite damaging, because even if you are careful, you will remove many of the useful bacteria that process waste products. For this reason it is important not to clean your filter when you make any changes to the tank, such as large water changes, change of food source or frequency, or introducing new fish. For events like these, a stable aquarium environment is vital, so leaving the filter alone for a bit longer can be helpful. Filters do need cleaning though so here is a quick run-through of how to do it properly.
Cleaning biological media
Sponges are usually used simply to trap waste particles and keep the water looking clean. Your fish however, are not really that bothered about how clean the water looks, since most come from streams and rivers full of particulate matter, but they are bothered about pollutants such as ammonia, which come from the waste products produced in an aquarium.
It is the bacteria that live in your filter which are responsible for converting pollutants like ammonia into less harmful substances, and many of these bacteria live on the surface of your sponges. Even if you have other media in your filter, a lot of bacteria are still living in the sponges so it is important to clean the sponges in a way that does not harm or remove too many of these bacteria.
Sudden changes in temperature, pH, and contact with antibacterial chemicals like chlorine will all kill useful bacteria, which makes tap water completely unsuitable for cleaning filter media. Instead, always use water from your aquarium. To clean your sponges, take a few litres of water from the aquarium (or from the filter if using an external), fill a container and gently squeeze out any waste until water runs freely and relatively clearly through the sponge. Solid biological media like ceramic pieces can be simply swished through the water to remove large build ups of waste.
The container you use should always be bought new, and only ever used for the aquarium. Never use a container which has been previously used for other purposes, since even if dried it may contain harmful chemicals. Once the media is clean it can be placed back in the filter, and the dirty water can be thrown away, or ideally given to your garden or houseplants.
Many fish keepers replace their media far too often, and this is usually a result of manufacturers suggesting regular replacements in order to sell more media. Sponges only need to be replaced when they loose their 'spring' or become miss-shaped, which is usually about every 12-18 months.
Biological media is about the same, but on both sponges and biological it is important that no more than 50% of your media is replaced at any one time. Replacing all your media means you are also removing all your bacteria, effectively shutting down any waste conversion, and will result in very dangerous levels of pollutants appearing in a short time.
If you replace a third of the media, the new media will 'seed' itself with bacteria very quickly from the remaining older media. Giving a gap of a few weeks, and replacing a third at a time you can safely replace all your media in a four-week period, although taking even longer is safer.
Media such as activated carbon or zeolite, which are sometimes referred to as 'chemical' medias since they remove unusual chemical pollutants from the water, will need replacing more often (usually every few months) and for these you should follow the manufacturers instructions. Shop around for replacements though, since you can get the same product for much less cost if you don't stick to the brand that came with your filter.
Using a filter to reduce nitrates
Filters usually focus on removing ammonia, nitrites, and visible waste and are not always designed to remove nitrates. In aquariums without significant plant growth nitrates can rise to dangerous levels, and can be difficult to reduce, even when using chemical medias and carrying out regular water changes. There is an easy way to use an external filter to remove nitrates however, but it needs to be done carefully.
The method is to allow one of your sponges to become clogged with waste, so that the water is forced to pass through 'tracks' in the sponge, leaving the rest relatively flow-free. What this does is causes most of the sponge to be in a oxygen-deficient state, so that normal filter bacteria, which require oxygen, are replaced by bacteria which use nitrates to obtain oxygen (nitrates are made up from nitrogen and oxygen).
It is important that the filter still maintains a fast enough flow-through so that oxygen in the water is available for the other bacteria living in the remaining sponges and biological media. To achieve this make sure you give the rest of the sponges and media regular maintenance, leaving just the one sponge clogged. Because several sponges and a sealed container are required, the method is only suitable for larger external filters.
Maintaining the impeller
Almost all aquarium water pumps contain an impeller. The impeller is a cylindrical magnet attached to a series of blades, which are used to move the water, and is normally fixed onto a metal or ceramic shaft and can be simply slid out for cleaning. Over time, algae, bacteria, and other debris can collect around the impeller, which will impede the performance of the pump.
Cleaning the impeller is relatively simple; a gentle rub with fingers or a cloth will remove most build-up. A pipe cleaner or cotton bud can be used to clean the housing and around the shaft. Impellers need only be cleaned every two or three months. It is a small job however, and can easily be done whenever the media is cleaned.
A dirty impeller will place a strain on the pump and considerably reduce its life span. In the vast majority of cases where filters or pumps break, it is a result of impellers not being cleaned regularly, and if this happens you may need to buy a whole new filter, since impellers are not always covered by guarantees.
Working out a schedule for your own filter and making a record of when it was last cleaned can help to make sure it gets done on time, and regular testing of ammonia, nitrites, and nitrates can be used to check your filter is performing properly.
1) Never replace all your filters media at once
2) Always use water from the aquarium to clean filter media
3) Never use any chemicals to clean your filter or its media
4) Never clean media in containers that have been used for anything other than aquarium use
5) Avoid cleaning the filter at the same time as introducing fish, changing foods, or doing large water changes.
6) Replace chemical media regularly, and check to see how much you pay for similar medias
7) Cleaning your impellor regularly will increase the life span of your filter
8) If you are buying a new filter, externals may be more expensive, but are much better and easier to use than internals
9) Always place the outlet of your filter at or above the surface, to re-oxygenate the returning water.
10) Never switch your filter off for more than a few minutes for maintenance.