What Does a Filter Do in a Fish Tank?

The Biology Of An Aquarium

Why should the water be filtered? When one analyses what occurs in an aquarium, the solution is fairly simple. A fish is a living entity that consumes, excretes, and “breathes” the water around it.
Fish waste products might be solid (for example, feces) or dissolving (eg urine, excess salt excreted from the gills).

Organic carbon molecules make up the majority of solid waste. Heterotrophic bacteria use oxygen while generating carbon dioxide. This technique may be problematic without proper oxygenation; yet, most aquarists prefer to remove solid wastes merely because they are ugly. Mechanical filtration is the primary method for removing solid waste. While this does clear the water, keep in mind that the solid wastes are not completely eliminated (and will continue to use oxygen) until the mechanical filter media is cleaned or changed.

Nitrogen is present in dissolved waste products in the form of ammonia and urea, which are also broken down into ammonia. Ammonia appears in two forms in water: The ammonium ion, NH4, and the compound ammonia, NH3. Although they are often referred to as “ammonia,” it is the NH3 form that is of the most important to aquarists. Ammonia in its ionic form is largely non-toxic to fish, however, the compound ammonia is very hazardous. The fraction of dissolved ammonia that occurs as NH3 is affected by water pH (a higher pH equals more NH3) and, to a lesser degree, temperature.

Ammonia is oxidized in an aquarium, much as it is in nature, by aerobic nitrifying bacteria such as Nitrosomas spp. and Nitrobacter spp. Nitrosomas spp. convert ammonia to nitrite by oxidation (NO2). Nitrite is still hazardous to fish, albeit not as much as ammonia. Nitrobacter spp. then oxidizes nitrite to nitrate (NO3). Nitrate is less hazardous than both nitrite and ammonia, but various fish react differently to it, with some sensitive to nitrate poisoning and others more resistant. Nitrate levels are toxic to corals and many animals.

Nitrosomas and Nitrobacter may be found in every aquarium. They are found in small quantities in the water but are mostly found on surfaces such as glass, pebbles, plants and decorations, and gravel. These bacteria will carry out ammonia and nitrite oxidation anywhere there is adequate oxygen. As a result, biological filtration is present in all aquariums. However, in order to retain more than a few tough fish in an aquarium, a larger number of these bacteria are required, as well as a steady supply of oxygenated water. This is what biological filtration is all about.

Most filters intended for mechanical or chemical filtration will also offer some biological filtration since Nitrosomas and Nitrobacter will grow on any appropriate surface. However, the presence of organic wastes will hinder biological filtration because heterotrophic bacteria would use available oxygen before nitrifying bacteria. Where there is a high concentration of organic waste, conditions might become anoxic (without oxygen), and biological filtration will end completely. In the worst-case scenario, anaerobic sulfur-fixing bacteria will begin creating very poisonous hydrogen sulphide.

As a result, the mechanical filtering medium should be cleaned or changed on a regular basis. Clearly, replacing the filter medium eliminates the biological filtering capacity. The ideal strategy to accomplish effective biological filtration is to have a biological filter medium that is not updated and does not accumulate organic waste, or that can be cleansed of organic waste on a regular basis without hurting the nitrifying bacteria.

The Role Of Water Changes

As previously stated, the end result of a biological filter is nitrate.

Nitrate is absorbed by algae and plants, which produces plant tissue, and by anaerobic bacteria, which produces nitrogen gas (N2), which escapes into the atmosphere. These bacteria are not often found in aquariums, and the circumstances are not conducive to the conversion of nitrate to nitrogen gas. Because many aquatic aquarium plants are unable to use nitrogen in the form of nitrate, nitrate tends to accumulate in an aquarium.

Excess nitrate in an aquarium is undesirable due to its potentially harmful effects as well as the fact that it promotes algae development and may harm attractive aquatic plants.

Nitrate can be removed from the water, although the procedures are impractical for most aquariums. Denitrators remove nitrate by converting it to nitrogen gas using anaerobic bacteria, however, they are often sluggish, costly, and inefficient. There are additional chemical filter media that absorb nitrate, however, they are both costly and inefficient. Algal scrubbers, which consist of a shallow, brilliantly illuminated aquarium full of algae through which water is circulated, may be employed. They are costly and complex to install, and although they are helpful in really large recirculating systems, they are not practicable for most home aquariums.

The only technique of eliminating nitrate that has been shown to be effective in home aquaria is that used in “Berlin” design marine tanks. Two layers of gravel separated by tiny mesh are placed atop a layer of low-oxygen water in these tanks. Small burrowing creatures keep the top layer of gravel oxygenated and waste products moving down to the bottom layer. Because this layer is not disturbed by burrowing, it loses oxygen, enabling de-nitrification to proceed. The water layer promotes gas exchange, avoiding total anoxia. While this procedure has been shown to be effective, it is tough to implement and cannot be utilized in freshwater.

In most circumstances, frequent partial water changes are the simplest and most effective technique to eliminate nitrate. Partial water changes will also aid in pH stabilization, the removal of various organic wastes, and the replacement of a variety of lost trace elements.

For these reasons, no matter how excellent your filtration is, partial water changes are always required.

What Is Filtration?

Mechanical, chemical, and biological filtration are all defined terms.

Filter, in its widest definition, is the act of passing water through some kind of filtration material. The goal is twofold: to maintain the aquarium clean for the hobbyist’s enjoyment, and, more significantly, to offer a proper habitat for the aquarium occupants.

Filtration is classified into three types: mechanical, chemical, and biological.

Mechanical filtration is the process of physically removing solid and suspended particles from water. Filter “wool” (really fiberglass), poly pads (a fibrous matting), and sponges are examples of the mechanical filtering mediums. More and smaller particles will be retained if a finer material is employed, although the filter medium may get clogged more rapidly.

Adsorption is used in chemical filtration to remove dissolved chemicals. Carbon and zeolite are the most prevalent chemical filtering medium. Chemical filtering may remove a variety of organic contaminants, dissolved metals, and chlorine.

The breakdown of waste items by naturally existing microorganisms is known as biological filtration. Biological filter media are not meant to break down these waste products, but rather to offer a broad surface area and ideal breeding conditions for these bacteria. Ceramic or siliceous noodles, plastic bio-balls, sand, and gravel are examples of the biological filter mediums. A biological filter media may be any inert substance with a wide surface area; the greater the surface area, the better.

The biological kind of filtration is the most essential in terms of fish health. If fragile species and marine fish are to be preserved, it is extremely necessary. Mechanical filtration is responsible for keeping the water pure and also for removing solid organic pollutants. Most mechanical filters also provide some biological filtering. Chemical filtration is not required, although it does assist to keep the water pure and may guard against the buildup of unwanted chemicals in an aquarium. Chemical filtration should not be used in quarantine tanks or when fish are being treated for illness since it removes drugs.

What Is “Good” Filtration?

To be effective, water must pass through the filter media (whether mechanical, chemical, or biological). More water flow equals more filtration, to some degree, but filtration is also affected by the surface area of the filter medium. The bigger the surface area, the higher the capacity to filter. Mechanical, chemical, and biological filtering are all examples of this. In coldwater and tropical tanks, the whole aquarium volume should be run through adequate filter material at least three times an hour for “excellent” filtration. A higher rotation rate, at least five times per hour, is required for marine tanks (see our marine fishkeeping tutorial for more information).

Greater water turnover is advised in smaller tanks (where there is less water volume to dilute harmful waste products) or while keeping big and/or dirty fish.

The magnetic impellor powered pump is by far the most popular means of moving water. These pumps are quiet, efficient, and cost-effective to operate. Water may be moved using an air pump: when air bubbles rise, they drag water up with them, generating circulation. However, as compared to the output of most impellor-driven pumps, the water turnover obtained by an air pump is minimal. Other drawbacks of air pumps include noise (even the quietest air pumps are far from silent) and expense (most air driven filters need regular filtering medium replacements).

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