What does a filter do in the aquarium ?

Do I need to buy a filter for my aquarium ? Do I need aeration ? What type of filter should I use from all the types on the shelf ?

A filter is essential to a well managed aquarium, unless you are changing water every day. What do filters do to the water, and why are there so many types available ? Can I buy a pump and filter, or should I get the HOB, or canister ? Aquarists here at Canada Aquaria have years of experience to rely on to give you insight into these questions. If you are looking at purchasing a filter or wonder what a filter does, post here.

Filtration

In an aquarium, we try to simulate what naturally occurs in the environment to cleanse and rejuvenate the water, in order to sustain a healthy fish population. In wetlands and swamps, a complex process occurs whereby water is filtered mechanically, biologically and chemically, to produce a rich medium for fish life.

In basic terms, an aquarium filter can be a simple mechanical box to a complex system which incorporates many subtypes of filtration, but the general idea is to filter out debris or waste from the tank.

A basic filter can be a box filter with floss hooked up to an air pump. The cost is minimal, about less than $20 for a small filter. The air pumps through the box filter and creates suction to draw debris into the floss chamber. This mechanical action remove the physical debris from the water (mechanical filtration). Over time the debris will break down using microorganisms.

Early on the in life of the filter approximately 5 to 7 days, nitrogen bacterial will develop to convert dissolved gas ammonia into nitrogen, via a complex biological action known as the nitrogen cycle. This is one of the most useful functions of an aquarium filter : to convert waste products such as urea and ammonia to less toxic compounds (biologic filtration).

Some filters will use carbon to absorb gasses and other dissolved chemicals from the water. This is know as chemical filtration. Other chemical methods can be used to accelerate extraction of chemicals from the water, such as reverse osmosis, chelation and oxidation.

What type of filter should I buy ?

There are many types of filters on the market. Depending upon the size of your tank, you are looking for output (amount of water filter per hour). In general the lowest output is with air pump driven filters, such as box floss filters and undergravel filters. Hang on back power filters range in size for 10 gallon aquariums and up to over 100 gallons. These are essential outside boxes with an impeller to draw water through an intake, filter across a medium pad, and then flow across an aerator. Canister filters are even higher output, and because they are enclosed, the pressure can be greater resulting in larger flow rates.

The type of filter that you buy comes down to personal choice and cost. Whether you use an air driven filter or a high tech canister filter, they are effective, some more than others. A simple sponge filter has worked well for decades, and is perhaps even simpler and most economical in terms of function and price. It is your choice, so research what you have in mind, based upon the size of tank (output), style (visible or not visible), cost and complexity.

Sponge filter : low cost, biologic and some mechanical filtration, highly visible, not very attractive, can be noisy.

Box floss filter : low cost, biologic and mechanical filtration, some chemical filtration when you are carbon, not very attractive, can be noisy.

Undergravel filter : low cost, biologic filtration only, requires gravel cleaning, invisible, difficult to maintain, can be noisy (air pump driven).

HOB (hang on back) Power filters : low to medium cost, high output, biologic, chemical and mechanical filtration, requires frequent cleaning, relatively quiet.

Canister Filters : medium to high cost, highly efficient, highest output and flow, biologic, mechanical and chemical filtration, requires frequent cleaning, quiet.

Ion filters, UV radiation sterilizers and protein skimmers are specialized filteration units to remove either microorganisms, chemical compounds and molecules to a desired water quality, usually for advanced aquarists. Diatom and water polishers are ultra high output filtration units, for ad hoc use by advanced aquarists.

Whenever filters are concerned, look for maximum customization abilities with media. Aquaclear hobs tends to have a large advantage in that regard vs most other hobs on the market. With the customizations most should go with some mechanical filtration and lots of biological filtration. The biological filtration is what will sustain your tanks and the mechanical helps keep the water clean. I personally run very little mechanical unless i have certain issues such as dirt or heavy particulates in the water. once it is cleaned up i remove the added mechanical filtration.

I think the average aquarist has unrealistic expectations for a filter. The name causes a problem - we see it as a water polishing device.
I think they work better when used as biological filters. You can remove debris withy a siphon, but you can't change water daily. So I am with Caoder on the 'how can you modify this filter' approach.

My favourite filter is an Aqua Clear, as it is really easy to modify and improve. Next in line come Aqua Nova, for the same reason (but the longterm quality is a mystery - new brand). I contend that any filter for which you buy inserts should be modified. Inserts go against all sensible approaches to filtration.

I have a deep and rational hatred of canisters, because of all filters, they are the ones that have to be manufactured with quality in mind. They aren't, and they break quite easily. The sturdy designs available just a few years ago have been replaced with fairly deliccate versions with cheaper parts, and that makes cleaning them a trip to the casino. They are expensive for what they offer. However, my canister experience is with fluvals, a terrible, brittle product. The more expensive models have a better reputation, but I go for the ease of cleaning that comes with a hang on the back filter (HOB in aqua-slang).

Most of my fishroom runs on a (fairly expensive) linear piston air pump, absolutely silent and built like a tank. I use a lot of corner box filters with a little bio media and floss in them. These filters don't filter a whole lot, but in a small tank with light stocking, they perform as major role. They make the water move. Sometimes filtration doesn't have to filter that much, if you have few fish and do weekly water changes. But stagnant water is low in oxygen, and that really affects our fish. An air driven filter bubbling away keeps some water flowing, and if you stock planted tanks at one small fish per two gallons or more as I do with my killies, it is ideal. Ditto for sponge filters.

If you watch any river, it moves. Water is rarely stagnant, and when it is, you don't see a lot of fish in it. Flow and current are really overlooked when we set up tanks. Look at your fish. A wide bodied air breather like a Gourami needs slow water, and because it surfaces to breathe, probably gets by on light filtration. An angel is like a sail, and will suffer in fast water. A torpedo shaped fish has evolved in fast water, and needs a flow. I stood in swordtail streams in Belize, and the flow just about knocked me off my feet in places. You could never match that in a home aquarium, since the box shape of a tank makes the water swirl rather than run in one direction. But you can also use your filters to meet torpedo shaped species' needs part way. For many livebearer species shaped like rockets, I use hob filters rated for 50 gallon tanks on 20 gallons. The fish love the oxygen, and their aggression vanishes when their energy can be put to what nature has meant it to be used for - swimming in fast water. I've controlled aggression in Cichlids, livebearers and others by upping the flow. So there's another use for a good, high flow filter. It makes tiger barbs behave....

I do like HOB filters but with the number of tanks I am running it is not cost effective so I now have a couple of large air pumps to run sponge filters and have varying degrees of satisfaction form them. I find that the round Hydor type of filters can be blocked up a bit and air flow will be compromised. A newer (around here anyway - they have been using this system in Europe for some time) is going with Matten filters.... these are sponges cut to fit one end of the tank and an air line fitted into a tube with an elbow going through the filter.... I find them very effective in my 23 longs, but I don't stock them heavily - there are usually only a pair or trio of dwarf cichlids for breeding..... but there is a nice flow through the tank and the aged sponge filter is great to allow fry a feeding ground... easy to maintain and there is not a lot of maintenance..... The current tends to collect most of the sediment at the bottom of the sponge and it is very easy to siphon it up when doing water changes.... I recommend that people give the concept a try.