What Does My Filter Do?
Filtering Your Aquarium Water
(The First Tank Guide)
Why Do I Need a Filter?
The purpose of the filter on your aquarium is to remove excess food, decaying organic matter, free-floating particulate, dangerous chemicals, and the fish's waste products from the water.
The fish excrete waste constantly as they swim around in the water. If this waste is not removed, the toxins that the fish are removing from their systems will rapidly build up to high enough concentrations that the fish will poison themselves. Early stages of this are called ammonia stress - when it becomes fatal, it is ammonia poisoning.
In addition, particulate floating in the water and decaying food and other organic matter can contribute to cloudy aquarium water if not kept in check.
These pages are provided to answer some basic questions about filters, including 1) what different filters are, 2) how different filters work, 3) what normal maintenance is required, and 4) what are some advantages and disadvantages to the filter type.
Biological filtration is absolutely necessary in any aquarium to
reduce the maintenance required. However, mechanical filtration and
chemical filtration both have their places. Mechanical filtration
helps maintain water clarity, and
chemical filtration can take care of problems with your source water or can be used to
remove specific toxins or any medication
that is introduced to the system.
It is important that you are aware that your tank water can be crystal clear and still be toxic to your fish, or it can be murky or dirty looking and be perfectly safe!
- Biological Filtration:
Biological filtration involves bacteria and other microorganisms (and to a lesser extent plants and some fungi) converting your fishes' waste into less toxic substances. Your fish excrete waste (they go to the bathroom) into their aquarium water constantly as they make use of the food they eat. This waste, if not removed, will become toxic to the fish. A biological filter will convert toxic ammonia (from your fishes' waste, excess food, decaying or dying plant mater, and dead fish) into Nitrite, and toxic Nitrite into Nitrate. Nitrate is relatively harmless, however, if it is not removed from the tank through regular water changes, Nitrate can cause kidney, liver and eye problems for your fish, as well as suppress their appetite and prevent their gills from absorbing oxygen from the water. Nitrate will also contribute to algae growth. Biological filtration occurs as the water passes over any surface that the bacteria processing the waste can grow on.
Biological filtration is established during a process called "cycling". Even the highest quality biological filters cannot process fish waste until they have properly cycled.
Plants can use some nitrogenous waste as fertilizer, though they will only be able to process this as they photosynthesize during the day. The concentration of nitrogenous waste used by plants will be so minimal as to make no significant difference in water quality. At night, however, plants respire just as animals do, and will be producing nitrogenous waste.
- Mechanical Filtration:
Mechanical filtration, also known as physical or particulate filtration, is provided by pushing the water through some form of filter media that acts as a strainer. This strainer will catch free-floating particles that cannot pass through the openings in the media. The media can be a sponge, filter floss, a dense mass of air bubbles (only in salt water), special filter pads, or even aquarium gravel.
The quality of the mechanical filtration will depend on several things.
First, how fine is the media? The finer the media, the smaller particles can be caught. However, finer media gets plugged much more quickly and either needs to be rinsed out or replaced often. Coarser media will allow more particles through, but will take longer to get plugged up. Many mechanical filters will use several layers of media, starting with coarse and ending with a fine media to provide optimal water cleaning.
Second, how much water is passed through the media? The longer it takes for the water to all go through the filter, the more time debris has to collect in the water or settle out, and the cloudier or murkier the water can become and the more debris will settle to the bottom of the tank.
Third, how often do you clean your filter? A mechanical filter will provide better filtration if it is cleaned frequently and appropriately. Damage to the filter media can greatly reduce the filter efficiency, and leaving a dirty filter cartridge plugged will prevent sufficient water flow or can force the water to flow around the media rather than through it, which will prevent the water from being filtered.
Also, how messy is your tank? The messier your tank is, the more you need mechanical filtration, however, the messier your tank is, the sooner your mechanical filter will become plugged. Some kinds of fish make a tank messier either by behavior (such as digging) or through their eating habits. Also, failure to provide sufficient water changes, over feeding, and other tank care issues will reduce the quality of your mechanical filtration.
Mechanical filtration can also be provided in a settling pool or sump. A settling pool is a container of slow-moving water that allows any heavy particles to settle out and collect on the bottom. This debris can be collected and removed with a siphon or with a net when the tank is cleaned.
- Chemical Filtration:
Chemical filtration is provided by carbon or chemical resins that extract toxins from the water. Activated filter carbon will aggressively remove chemicals from your water until the carbon becomes saturated. It is very important that any activated filter carbon in your filtration system be changed often.
Typically, about 1 cubic inch of activated filter carbon can provide chemical filtration of 2 gallons of water for up to a month, however, in order for this to work several conditions must be met:
- Water flow
- You should move the entire tank volume in water through your carbon at least twice an hour. If your water is not moving this quickly, it is not being exposed to the carbon often enough and will not have chemicals removed sufficiently.
- Chemical load
- Water that is abnormally hard, very soft, chemically softened or hardened, or that has high concentrations of minerals or trace elements will saturate your carbon more quickly. Also, adding plant foods, trace elements, or mineral supplements to your water will also saturate your carbon faster as the carbon removes these chemicals from your water.
- Water changes
- Insufficient water changes will allow for buildups of chemicals in the water which will increase the burden on your chemical filtration.
- Tank load
- Overpopulated tanks will also increase the load on your chemical filter, as well as any other filtration you have.
You should also keep in mind that carbon engineered for aquarium use does not remove ammonia, Nitrites, Nitrates, carbon dioxide, or oxygen.
Other resins are available on the market now, some of which remove specific chemicals or chemical compounds, others work the same way as carbon. Carefully review the packaging on these products to be sure you use them properly and that they can actually help with the problem you are experiencing. Many resins can be recharged, often using common household methods (such as soaking in a salt bath). Methods for recharging chemical resins will vary and should be listed (if applicable and safe) on the manufacturer's packaging. Also, some resins need to be primed or charged prior to use. It is very important to the health of your fish that you completely read the entire manufacturer's labeling and packaging before attempting to use any chemical resins to help filter your water, as some chemical resins can be lethal to your fish if not properly primed or charged.
It is vitally important to the health of your fish that you provide them with sufficient filtration. Filtration can make your tank look nicer and will greatly reduce the care required to keep healthy happy fish (a 10-15% water change once a week in a filtered system is much nicer than the 80-90% a day that an unfiltered system needs to stay viable). But filtration is no excuse to shirk on tank maintenance. Your fish will still need proper feeding, tank cleaning, water changes, and regular inspection for abuse, stress, disease, or any other problems.
There are many varieties of filters, including both submersible and non submersible models. You should select a filter that will fit your filtration needs and be appropriate for the type of fish you are keeping. Having multiple filters on a tank will usually give the best results and will provide backup in case of an equipment failure.
More information is available on these types: Hanging or power filters, corner or box filters, under gravel filters, sponge or breeder filters, canister filters, fluidized bed filters, trickle filters, and rotating drum filters. I also have information on protein skimmers (saltwater only) and Ultraviolet Sterilizers.