Freshwater Aquarium Filter systems are essential

The lakes and oceans of the world are large enough to be balanced ecologically. Fish waste is all consumed biologically; there is no build up of ammonia, nitrites and nitrates making the water toxic. Fish populations adjust according to conditions they have no need for a freshwater aquarium filter.

A freshwater aquarium on the other hand is miles away from being a natural environment. Without a freshwater aquarium filter a tank with even a moderate population of fish will quickly become foul and kill all of the inhabitants. Even with an adequate freshwater aquarium filter, the water in an aquarium needs to be changed regularly because fish in the numbers that aquarists like to fill their tanks with produce far more waste than the resident bacteria can possibly cope with.

How does a Freshwater Aquarium Filter Work

Ok, so you must have a freshwater aquarium filter. You have a choice but any freshwater aquarium filter you are considering for your tank should perform in three ways – mechanical, chemical, and biological.

  • Mechanical filtration uses foam or filter fibre to remove large particles, like uneaten food and fish excrement. Mechanical filters are graded from coarse to fine, with fine filters trapping the smallest particles.
  • Chemical filtration includes activated carbon and various ion exchange resins. Activated carbon traps dissolved organic compounds that are not removed by any other means (except water changes). Ion exchange resins are specific for one type of ion. Generally speaking most freshwater aquarists will have little need for ion exchange resins except perhaps for copper.
  • Biological filtration uses colonies of helpful bacteria to break down the waste products produced by fish and overfeeding. Fish waste and food ultimately break down to ammonia (NH3), which is extremely toxic to fish even at low concentrations (~5-10ppm). Some bacteria are able to metabolise ammonia into nitrite (NO2-) – also very toxic, another type of bacteria is able to convert nitrite into nitrate (NO3-), which is much less dangerous. While fish can endure some level of ammonia and nitrite, it is not conducive to the long-term health of the fish. Even in non-lethal doses, these pollutants are still a source of stress, and in an aquarium any source of stress weakens the fish and makes them vulnerable to bacterial and fungal infections. This is why an aquarium must be fully cycled before adding fish. The shock of moving into a new home is stress enough without having that home toxic as well!

What freshwater aquarium Filters are Available?

  • Undergravel (UGF) filters consist of a grid of plastic pipes with small holes every half inch or so. This grid sits under the gravel or substrate of the aquarium, creating a space of water beneath the gravel. The pipes are all connected to up to four ‘air lifts’ which slowly pull detritus and debris down through the substrate. The idea is that bacteria can break it down there. The advantages of UGFs are that they are very cheap and easy to setup and run, and the aeration helps keep dissolved oxygen high. One disadvantage is that they normally do not do chemical filtration. As well as this the small holes in the filter get blocked and waste tends to accumulate because it is not all broken down. It is therefore necessary two or three times a year to clean the filter. This involves scooping out all of the substrate to get at the filter. For this reason alone, undergravel filters are becoming less common.
  • Canister filters are a much better choice. These units consist of a canister and pump with a siphon tube to pull water out of the tank and a return tube to pump the water back in. The typical canister normally contains some type of coarse mechanical media, like ceramic “donuts” or very coarse fibre, some chemical media like filter carbon, some porous glass or stone for biological filtration, and finally some very fine filter fibre. So a canister filter actually does all three types of filtration. Most canister filters are very thorough and do a great job keeping aquarium water clean. The downside to these filters is that they tend to be expensive, use expensive media, and if not maintained well they can become nutrient traps. This means that all of the fouled filter media actually begins adding nitrogenous waste back into the water instead of removing it. Algae blooms and poor water quality are the result! Also, since canisters are completely closed, they do not oxygenate the water so it becomes necessary to add an airstone or perhaps a small water pump to aggitate the water surface. Overall though, when properly maintained, a good canister filter is hard to beat.!
  • Power filters hang on the outside of the tank and use a pump to pull water up into the filter. The water then passes through mechanical, chemical, and biological media in various configurations, then spills back into the aquarium. These filters are rapidly gaining popularity with aquarists because they are efficient, slightly less expensive than canisters, and a dream to maintain. Since they are exposed to the air they help oxygenate the water. The oxygen-rich water helps support huge populations of nitrifying bacteria making power filters some of the most efficient biological filters. The biowheel version is particularly good.
  • wet/dry or trickle filter. These are only mentioned for completeness. They are essentially used for very large tanks. They are expensive and if they go wrong can empty your tank!

So there you have it. You can now make an informed choice when considering your freshwater aquarium filter. You have basically three choices of freshwater aquarium filter and you definitely need one of them.