An aquarium filter is an absolute essential. It is the heart of your tank. The filter not only keeps your water clean (mechanical filtration) but also neutralises the harmful chemicals your fish produce like ammonia (biological filtration). Your filter must stay on permanently. Before adding fish to any aquarium the filter needs to be ‘cycled’. Once cycled this will prevent harmful chemicals from killing your fish. Read cycling your aquarium.
Types of filters
Filters come in different forms, but it really depends on how large your tank is, and your budget. For tanks on the smaller side, a small submersible filter that sits inside the tank can be sufficient, or a HOB (Hang on back) filter. However when dealing with larger tanks most people prefer the external canister filters. These are much larger and hold much more filter media. To keep the filter in good condition you need to clean the impeller as this is normally the cause of failure. The small propellers are normally held in place via a magnet that can be easily taken out. Submersible filters are probably the quietest, but take up the most room as they sit inside the tank.
Filter media is what we call the sponges and ceramic rings that sit inside the filter. The more media, the more beneficial bacteria you will have growing. This is why canister filters are preferred. Filter media can be used permanently and shouldn’t be replaced until it’s literally falling apart, unless it’s active carbon. Manufacturers will state that sponges need to be replaced every couple of weeks etc, but this is often false and won’t need to be replaced unless they clog and can’t be cleaned. If you need to replace any filter media, never replace it all at the same time. Replacing all of the media will restart the cycle.
Another type of media is active carbon. Carbon comes with a lot of filters. It can be used to keep your water crystal clear, but needs to be changed on a regular basis, as it does run out. Carbon can remove things like heavy metals and previously dosed medication. Carbon doesn’t need to be added, as it can become quite expensive to keep replacing. A lot of people remove the carbon straight away.
Do not clean your media in tap water when cleaning. The chlorine will kill off the beneficial bacteria, resetting the cycle. You can rinse your filter media in something such as a bucket of old tank water.