Importance of Filtration
There is a lot of “stuff” that makes up the water in an aquarium. Of course there is pure water (H20), but there are other molecules, trace elements, humic substances, fish waste, bacteria (good and bad), fungal spores, and microorganisms. Some of these things are good to have in your water and some are not. Most are fine to have in moderation. The main way we as aquarists are able to keep everything in balance is through proper filtration of the water.
Types of Filtration
When most people think of an aquarium filter, what they are picturing is the good old hang-on-back filter (HOB). They don’t necessarily think about the different kinds of filtration this unit is responsible for. In a freshwater aquarium there are three basic categories of filtration: mechanical, biological, and chemical.
Mechanical filtration is simply separating debris from the water. Fish waste, bits of plant and food material. It is the physical removal of “stuff” from the water. Most means of mechanical filtration involve passing water through a fine mesh or sponge. The sponge or mesh needs to be periodically cleaned to remove the unwanted material and to allow water to flow more freely.
Examples of Mechanical Filters:
Reverse Osmosis (RO)
Reverse Osmosis is a specialized form of mechanical filtration. Many aquarists with very hard water employ it to remove minerals and other small substances from the water before it goes into the aquarium. It works by pumping water at high pressure through an incredibly tight mesh-like membrane. It is possible to produce nearly pure water from this process, and because of this any beneficial trace elements, nutrients, etc… need to be added to the water afterwards. RO water can be purchased at fish stores. You can also install an RO unit in your home, but the cost may be prohibitive. Here are some examples of Reverse Osmosis Equipment.
Biological filtration is the sort of filtration done by plants, algae, and bacteria in the aquarium. When we talk about a tank being “cycled” we are talking about having established an adequate colony of beneficial bacteria. These bacteria convert harmful Ammonia to the relatively benign Nitrate. The beauty of bacteria is that they will attach themselves to all surfaces within the aquarium. Basically this turns every object in the aquarium into a mini-biological filter. For more information about how bacteria filter water, see my page on The Nitrogen Cycle.
Plants and algae too can remove harmful material from the water. Plants will take up excess heavy metals and other toxins into their tissue. They also readily take up Ammonium and many will also take up Nitrates. Algae also consume Nitrates and Ammonium as well as other toxins.
Sponge filters make excellent surfaces for beneficial bacteria to adhere to and colonize. These are the sponge filters I use in my aquariums:
- XINYOU XY-2830 Aquarium Bio-Sponge Filter
- XY-380 Aquarium Fish Tank Biochemical Sponge Filter, 4-1/2-Inch
- Jardin Aquarium Fish Tank Mini Biochemical Sponge Filter
- Oksale Aquarium Biochemical Sponge Filter Filtrator Percolator XY-168
Chemical filtration is a way of cleansing water by binding unwanted compounds to filter media. Activated charcoal is a typical material used for this. You can find it in household water filters. It binds to many different kinds of compounds, both good and bad. This means that plant fertilizers, medications, and other compounds you actually want to keep in an aquarium may be filtered out by chemical filtration. There are some chemical filtration media that are designed only to filter out certain things. A commonly used form of chemical filtration is Purigen Filter Media.
UV Sterilization is a unique kind of filtration. It works by passing water through a tiny compartment that is illuminated by UV light. The light kills many microorganisms like algae, bacteria, and parasites. UV equipment can be very compact and easy to install, especially when attached in-line to a canister filtration system. Here are some examples of UV Sterilizing Equipment.
I did not include this with the three main types of filtration, because unlike the others, it is not always necessary.
The problem with UV sterilization is in situations like “green water”. Green water is an algal bloom that can make the water turn a thick, green color. The UV sterilizer will eventually clear up the water, but it does not cure the cause of it.