Aquarium Filtration Overview

As soon as fish are added to an aquarium, the normal processes of respiration and digestion produce waste products that pollute the water. There are also other sources of pollution, such as decaying uneaten food.

The biggest challenge in keeping an aquarium is controlling the level of these pollutants so that your fish have a healthy environment. One of the things you need to meet that challenge is an effective aquarium filtration system.

In many ways, aquarium filtration is the most complicated and difficult aspect of fishkeeping. A visit to any well-stocked aquarium or pet store will reveal an astonishing array of filters that vary widely in design and price.

In addition, the beginning aquarist faces a lot of new terms that are used to describe filters. Understanding how filters work and what they accomplish can make it much easier to sort through everything.

You may assume that the basic goal of filtration is to remove debris floating in the water so that it doesn't cause pollution. While this is correct, it's only part of the story.

This process is mechanical filtration. If mechanical filtration is sufficient, very little solid matter will be left floating in the water. However, just because the water looks clean doesn't mean it is safe for fish.

Chemical Aquarium Filtration

Chemical aquarium filtration is needed because a number of dissolved, invisible compounds accumulate in aquarium water and they can't be removed by mechanical filtration. These compounds are not toxic to the fish but can inhibit their growth and cause chronic, low-level stress that eventually leads to disease. Most of these compounds are dissolved organic substances produced by natural biological decay.

The dissolved organic substances eventually reach concentrations high enough to become visible as a yellowish tinge in the water. You can see this when a sheet of white paper is held behind the tank so that half of it is viewed through the water. If the water is healthy for the fish, the paper viewed through the water will be as white as the other half; if not, the paper will have a yellowish cast to it.

Chemical filtration removes many, but not all, of these compounds. However, some substances that affect the growth of the fish can only be removed by making partial water changes on a regular basis. If this isn't done, the fish will never grow to normal adult size. This stunted growth will result in fish that never achieve the beauty of mature fish, and it can cause other related health problems.

Biological Aquarium Filtration

Biological aquarium filtration is the most important of all. The lack of effective biological filtration is probably responsible for the deaths of more fish than any other cause. The particular dissolved compounds controlled by biological filtration are very toxic to fish even at low concentrations.

In newly set up tanks, the effects of these compounds can kill fish very quickly. In aquariums that have been running longer but are overstocked with fish, there can be constant low levels of these compounds in the water. This creates chronic, long-term physical stress, resulting in diseased and dying fish.

To understand biological filtration, it is necessary to understand a basic process in the aquarium: the nitrogen cycle. Ammonia is one of the key elements in the nitrogen cycle. Fish produce ammonia directly both as a by-product of respiration and as a waste product from the digestion of foods.

Solid wastes are also converted into ammonia, which is why it is important to remove them with mechanical filtration. Uneaten food, plant materials, and other organic items that decay in the tank are also converted to ammonia. Ammonia, a nitrogen-based compound, is extremely toxic. In an aquarium, it can build up quickly and threaten all the fish in the tank.

Aquarium Filter Designs: Box, Power, and Canister Filters

Mechanical aquarium filters all serve the same function, but they come in a variety of different designs: inside box filter, inside power filter, outside power filter, and canister filter. Each type of filter has its own system for creating water flow, and each type has its own advantages and disadvantages. All will work well depending on the capacity of the filter, the size of the tank, and the amount of maintenance the filter receives.

  

Nearly all mechanical filters also have a compartment to hold activated granular carbon, so that they act as efficient chemical filters as well.

To avoid having the carbon become covered with solid matter, which would keep it from adsorbing the chemical wastes, the water should pass through the mechanical filtering material first. That way, the solid matter will be removed from the water before it reaches the carbon.

The inside box filter is the simplest and least expensive of all mechanical filters. The filter is set up inside the aquarium itself, and it can be relatively effective in smaller tanks.

Bubbles from a tube or air stone inside the box draw water through it. The bubbles rising to the surface from the box also help aerate the tank. The box itself is filled with Dacron filter material and a quantity of granular activated carbon.

There are a few drawbacks to the inside box filter. It is not very effective in large aquariums. From a visual standpoint, it adds nothing to the appearance of the tank, although it can sometimes be hidden successfully behind plants or a large rock. Also, changing the filter material requires removing the unit from the tank.

Aquarium Filter Designs: Undergravel Filters

Biological aquarium filters, including under-gravel filters, function in a completely different way, and they have a completely different design. The Nitrosomonas and Nitrobacter bacteria necessary for biological filtration will colonize virtually every surface in a tank. However, there is usually not enough surface area in a tank to support populations of these nitrifying bacteria large enough to process all the ammonia that is produced in a typical aquarium.

 

A biological filter deals with this problem by making the natural nitrogen cycle operate more productively.

A biological filter has two main functions. It increases the amount of surface area available to the nitrifying bacteria, and it creates a constant flow of aquarium water over the colonized area.

The most popular kind of biological filter is the undergravel filter. It is relatively inexpensive, reliable, and very effective. An undergravel filter is really just a plastic plate that covers the bottom of the aquarium. The plate has many small holes or slots in it. The exact physical appearance varies from one brand to another, but all work on exactly the same principle.

The undergravel filter plate is covered with aquarium gravel. Located at each back corner of the plate is a lift tube that extends from the plate to the top of the tank.

Other Important Aquarium Items

There is a large variety of other aquarium items and accessories available for aquarists to choose from, but only some are absolutely necessary. You will want to have enough air line tubing to run between the air pump and the air stones, as well as some extra air stones. Over time, air stones begin to clog, which reduces their efficiency and causes unnecessary wear on the air pump.

You should also have an extra set of replacement diaphragms on hand for the air pump. If not, your dealer can replace them for you when they wear out. Some hobbyists like to be prepared for larger problems. If you are willing to make the investment, a back-up pump and even an extra heater or filter provides insurance against equipment failure.