Sterilization

Sterilization as a form of filtration is normally employed in the marine aquarium, although there are situations when it can be useful in a freshwater aquarium. The process involves passing water through a pressurized unit containing an ultraviolet (UV) lamp. UV light at the right intensity is able to break down some algae cells and disease organisms, with obvious benefits for aquatic life. However, as with chemical filtration, it can also destroy useful elements. In general, because of the expense of UV sterilizers and their relatively limited use, they are not necessary in planted aquariums. Do not confuse UV sterilizers with UV clarifiers, which work on the same principle, but allow for a greater space between the water and the UV light, so that only algae cells are affected, not disease organisms.

foliage of fine-leaved species. This prevents light from penetrating the chlorophyll cells, reducing their ability to photosynthesize. A buildup of organic debris in the aquarium may also encourage the growth of algae and increase the number of disease-causing bacteria in the aquarium.

Reverse osmosis (R.O.) water is also produced by a mechanical filtration unit, although in this case the sponge is replaced by an incredibly fine membrane. This removes almost all the contaminants (meaning everything other than water molecules - H20), leaving almost pure water. Reverse osmosis units are particularly useful when keeping softwater fish, which prefer slightly acidic water containing very few minerals. However, R.O. water is not suitable on its own for fish or plants because it is deficient in some of the important elements of water that provide a stable and useful environment. R.O. water must be mixed either with normal tap water or a chemical "buffer" that introduces trace elements and carbonates to stabilise pH.

Water changes are another form of mechanical filtration as they constitute a physical method of removing substances.

Biological filtration is the most important type of filtration, especially for fish. It takes advantage of the natural process whereby living organisms (bacteria) remove or convert toxic substances (ammonia or ammonium) into less toxic substances. The filter medium has a very high surface area (meaning that under a microscope it would appear very porous rather than smooth) that is colonized by naturally

Above: A commercial R.O. unit produces water with a pH of 6.5-7 and no hardness. Buffers, trace elements, and nutrients must be added to it before it is able to sustain plant and fish life in the aquarium.

occurring bacteria. As the aquarium water passes through the media, the bacteria remove ammonia by oxidation, creating nitrite (N02). The nitrite is then converted by other bacteria into less toxic nitrates (N03), which are released back into the aquarium. In some cases, anaerobic bacteria (meaning that they thrive in low-oxygen conditions) will obtain oxygen by converting nitrates into nitrogen gas (N03 to N2), which then escapes through the water surface into the atmosphere.

Biological filtration is of greater importance to fish than it is to plants because plants readily use ammonium and nitrates as a source of nitrogen for their own needs. However, ammonia is dangerous to both plants and fish, so biological filtration is still required in a planted aquarium. The difference between ammonia and ammonium is discussed on page 73, but in aquariums where ammonium occurs in preference to ammonia, plants perform much of the function of a biological filter. This is one reason why living plants are a practical, not just aesthetic, addition to many aquariums.

Chemical filtration removes chemical substances from the water using a medium that binds chemical compounds to itself. This binding is called adsorption and a chemical filtration medium is described as an adsorptive medium. Most chemical media are indiscriminate and will adsorb a wide range of compounds, both good and bad. They remove not only toxins, such as heavy metals, nitrites, and nitrates, but also useful compounds, such as nutrients and many aquatic treatments. For this reason, chemical filtration is best employed as a temporary form of filtration. It can be very useful in the removal of disease or algal treatments, once these have done their job, to remove heavy metals such as copper, etc., and to filter rainwater or tap water before they are added to the aquarium.

Plants convert light, carbon dioxide, and nutrients into biological matter.

Plant material and proprietary foods are consumed by fish.

Fish waste is excreted directly and indirectly as ammonia (NH3), which is highly toxic.

Nitrosomonas bacteria in the filter and aquarium substrate use oxygen to break down ammonia into nitrites

Harmful Nitrate Level For Freshwater

The majority of nitrates are removed by water changes, although some are converted by substrate bacteria.

Nitrates are toxic only at high levels and are partially taken up by plants as a source of nutrients.

Nitrites are slightly less toxic than ammonia, but still poisonous, even at very low concentrations.

Nitrobacter bacteria in the filter and substrate break down nitrites into nitrates (N03).

The majority of nitrates are removed by water changes, although some are converted by substrate bacteria.

Plants convert light, carbon dioxide, and nutrients into biological matter.

Plant material and proprietary foods are consumed by fish.

Nitrates are toxic only at high levels and are partially taken up by plants as a source of nutrients.

Nitrites are slightly less toxic than ammonia, but still poisonous, even at very low concentrations.

The nitrogen cycle

In anaerobic conditions in the substrate, and sometimes in the filter, anaerobic bacteria break up nitrates to obtain oxygen, thus releasing nitrogen gas.

Nitrobacter bacteria in the filter and substrate break down nitrites into nitrates (N03).

Fish waste is excreted directly and indirectly as ammonia (NH3), which is highly toxic.

Nitrosomonas bacteria in the filter and aquarium substrate use oxygen to break down ammonia into nitrites

Canister Filter Basic Principle

Above: An external power filter can sit beneath the tank. Place the return at the water surface, or lower down if you wish to reduce oxygen levels in a planted aquarium.

Right: Large external power filters house mechanical, biological, and chemical media. Water passes through the media and is returned to the tank via an outlet tube.

Types of filtration unit

Several types of filter are available for aquariums, although most work on the same basic principle, providing mainly mechanical and biological filtration. In most cases, water is drawn by a pump through a canister containing filtration media. Most filters are based on either internal or external designs. An internal filter is a compact unit that usually contains a sponge medium used for both mechanical and biological filtration. An external filter also uses sponge media, but because it is placed outside the aquarium it can be much larger without taking up space in the aquarium. The extra space available in the canister of an external filter allows you to use a wide range of media, which makes an external filter much more flexible and adaptable to the needs of the aquarium.

Because the bacteria that perform biological filtration require high amounts of oxygen, most filters have a high flow

Chemical filtration media rate, allowing water to pass through the filter before the oxygen is used up. The water released from the filter outlet is lower in oxygen than when it entered the filter, although often, the surface agitation caused by the pump will quickly cause the aquarium water to become reoxygenated. Therefore, even though the bacteria in the filter are using up oxygen, filters will generally introduce sufficient oxygen into the aquarium. In some cases, this can cause problems for aquarium plants, because high oxygen levels make It difficult for them to assimilate nutrients. In a planted aquarium, it is sometimes best to use filters with lower flow rates, or undersized external filters to reduce the surface movement and keep oxygen levels low. Lowering the outlet of a filter will also help to reduce surface movement in the aquarium.

Aquarium filters

Below: An internal power filter is ideal for the small aquarium. It consists of a sponge to provide mechanical and biological filtration and a pump to circulate water.

Right: Large external power filters house mechanical, biological, and chemical media. Water passes through the media and is returned to the tank via an outlet tube.

Compartment for activated carbon to remove discoloration and pollutants.

Above: An external power filter can sit beneath the tank. Place the return at the water surface, or lower down if you wish to reduce oxygen levels in a planted aquarium.

Fine media can be placed inside a permeable net.

This medium is designed for phosphate removal.

carbon is a popular all-purpose chemical medium.

Zeolite-based media remove nitrates and can be recharged.

carbon is a popular all-purpose chemical medium.

This medium is designed for phosphate removal.

Fine media can be placed inside a permeable net.

Zeolite-based media remove nitrates and can be recharged.

Below: An internal power filter is ideal for the small aquarium. It consists of a sponge to provide mechanical and biological filtration and a pump to circulate water.

This pump unit powers the filter. Clean the impeller periodically.

Filtered water returns to tank here.

Compartment for activated carbon to remove discoloration and pollutants.

This pump unit powers the filter. Clean the impeller periodically.

Filtered water returns to tank here.

Sponge traps particles and harbors beneficial bacteria.

Some internal power filters contain additional biological and chemical media in separate compartments.

Sponge traps particles and harbors beneficial bacteria.

Some internal power filters contain additional biological and chemical media in separate compartments.

Clean and dirty filter sponges

Relatively clean filter sponges provide an ideal surface for bacteria to colonize and are the basis of biological filtration.

Allowing one of the sponges to become clogged will encourage anaerobic bacteria to grow, which helps to reduce nitrates.

Below: Sponges should be cleaned only in water from the aquarium. Tap water contains chlorine, which may kill useful bacteria. Rinse sponges lightly; a slightly dirty sponge is more effective than a brand new one.

Relatively clean filter sponges provide an ideal surface for bacteria to colonize and are the basis of biological filtration.

Allowing one of the sponges to become clogged will encourage anaerobic bacteria to grow, which helps to reduce nitrates.

Below: Sponges should be cleaned only in water from the aquarium. Tap water contains chlorine, which may kill useful bacteria. Rinse sponges lightly; a slightly dirty sponge is more effective than a brand new one.

Dirty Sponge

Anaerobic bacteria

If a filter with a relatively high flow rate is regularly cleaned and maintained, it will provide plenty of oxygen for the denitrifying bacteria within it. If the filter has a slower flow rate or becomes clogged, anaerobic conditions will appear in the filter and denitrifying bacteria will not be able to survive. In an anaerobic environment, different forms of bacteria will emerge that source oxygen from compounds such as nitrates. In this instance, the bacteria use up nitrates and release nitrogen gas, which escapes at the water surface.

If a filter is properly maintained, it is possible to sustain colonies of both aerobic and anaerobic bacteria that together will reduce ammonia, nitrite and nitrate levels in the aquarium. Although nitrates are used by plants as a source of nutrients, they require only about 1-2mg/l in nature; high levels (above 30mg/l) can be damaging to some plants. Fish can normally tolerate much higher levels of nitrates, so anaerobic filtration has minimal benefits to fish but can be an important method of nitrate removal in planted aquariums. To encourage both aerobic and anaerobic bacteria in filters, allow part of the filter to clog, but keep the rest relatively clear. A simple way of doing this is to have a "clean" sponge and a "dirty" sponge in the filter. First, water passes through the clean sponge, where aerobic bacteria will reduce ammonia and nitrites and produce nitrates. Next it passes through the dirty sponge, where the nitrate is converted to nitrogen gas.

When you come to maintain the filter, either swap the sponges around (by cleaning the dirty sponge and leaving the clean one to become clogged) or wash the clean sponge, but only rinse the dirty one lightly. In larger external filters, you can use a number of sponges and swap them alternately.

Plants as filters

Aquatic plants also form part of the filtration process in well-planted aquariums. The uptake of metals and nitrogen compounds by plants and the release of oxygen has a significant effect on the overall water quality of the aquarium. In some larger outdoor ponds, plants are actually used as part of the filtration process. In these cases, water from the pond is allowed to pass through or over a large bed of aquatic or bog plants. The plants reduce nitrate and/or ammonium levels and remove heavy metal compounds that may be damaging to fish and other animals. Because plants have little control over the amount of metals they assimilate, they are often used to remove toxic metals from water sources. In the aquarium, plants are especially useful in removing metals such as copper, which may be "left over" from aquatic treatments. If the function of plants and anaerobic bacteria are included in the nitrogen cycle, filtration in a planted aquarium becomes more complex and efficient. The dangerous compounds of metals, ammonia, nitrites, and nitrates are reduced to such low levels that you no longer need to carry out water changes so frequently. However, water changes are still important for other reasons, so they should never be entirely excluded from regular maintenance.

Water hardness

Water is often described as hard or soft, and these terms relate to the amount of dissolved salts and minerals present in the water. A high concentration of salts and minerals results in hard water, while a low concentration produces soft water. Usually, it is the calcium and magnesium salts that determine overall water hardness. In natural water supplies, hard water usually contains more nutrients than soft water, which is an advantage to aquatic plants. However, hard water generally contains less carbon dioxide and other nutrients in an available form, so plants that are not accustomed to hardwater conditions may not do very well in them. A preference for water hardness varies according to species, and in the aquarium it is quite common for aquarists to mix hard- and softwater species together. Providing you avoid extremes of water hardness, the majority of plants will do well in medium-soft water with additional carbon dioxide.

Water hardness is often linked with pH, and many of the elements that cause high water hardness also cause a high pH

level. However, the two are only loosely connected and it is often possible to achieve high pH levels with soft water.

Acidity / alkalinity (pH)

Water is made up of positively charged hydrogen ions (H+) and negatively charged hydroxyl ions (OH"). The pH level is a measure of the ratio of these two ions in a body of water. Acidic water has more hydrogen ions, while alkaline water contains more hydroxyl ions. Neutral water contains an equal ratio. pH is therefore a measure of how alkaline or acidic the water is. Some fish, such as the Rift Lake cichlids, prefer alkaline, or high, pH conditions, while discus or dwarf cichlids prefer acid, or low, pH conditions. pH is measured on a scale of 1-14, with 7 being neutral. Anything below 7 is acidic and above 7 is alkaline. Aquarium fish generally live in

Below: Floating plants and fast-growing species, such as this Myriophyllum sp., will take up nutrients and chemicals quicker than other plants, thus providing a useful service in maintaining water quality in the aquarium.

Below: Floating plants and fast-growing species, such as this Myriophyllum sp., will take up nutrients and chemicals quicker than other plants, thus providing a useful service in maintaining water quality in the aquarium.

Fish Tank Floating Plants Types

How pH is measured

Water (H20) is made up of positively charged hydrogen ions (H+) and negatively charged hydroxyl ions (OH'). The pH level is a measure of the ratio of these two ions in a body of water. Acidic water has more hydrogen ions; alkaline water more hydroxyl ions. Neutral water has an equal number of both.

WATER MOLECULE Hydrogen

Oxygen

Oxygen

Hydrogen

Hydrogen

Hydrogen ion +

The pH scale

Hydroxyl ion

Hydroxyl ion pH 7: neutral.

The pH scale is logarithmic, meaning that each unit change in pH, say from 7 to

8, is a ten times change. A change of two units from 7 to 9

is a hundred times change, and from 7 to 1 0 reflects a thousand times change. This is why a sudden change in pH is very stressful and harmful to fish.

pH 9: 100 times more alkaline than pH 7.

pH 8: 10 times more alkaline that pH 7.

pH 7: neutral.

Fish and plants thrive in a well-buffered tank.

Minor pH fluctations are not a problem.

^ With no carbonates and/or buffering capacity, any acids produced will lower the pH level. This can happen quickly, causing death to fish and damage to plants.

Sudden drop in pH can be life threatening.

Buffer

Acids

Fish Aquarium Acid Levels

Buffer water with a pH of between 5 and 9; very few fish will survive happily in water with a pH level outside this range.

The pH level is closely linked to levels of carbon dioxide in the aquarium, because carbon dioxide produces carbonic acid, which is acidic and lowers pH. The pH in most aquariums will drop over time due to the acids produced by waste organic matter, respiration, and filtration processes. Regular removal of waste matter and regular water changes will reduce this effect. pH changes are damaging to fish and plants only if they happen suddenly. Because carbon dioxide and organic-rich substrates are used in planted aquariums, the water is more often slightly acidic than alkaline, although fluctuations occur within a 24-hour period due to the photosynthetic and respirational effects on carbon dioxide and oxygen concentrations in the water.

Buffering capacity

Buffering capacity describes the ability of a body of water to maintain a stable pH level, or more accurately, to withstand drops in pH levels. Water contains buffers, often In the form of carbonates, that reduce fluctuations in hydrogen ions, thereby reducing any severe drops in pH. Buffering capacity is closely linked to water hardness and the same substances apply for both parameters. Hard water is generally better buffered and has a higher alkalinity (pH) than soft water. The buffering capacity of water can be kept stable by regular water changes. It is vital that carbonate hardness is regularly measured in planted aquariums, as the use of C02 can reduce the aquarium's buffering capacity and/or hardness. If all the available carbonates are used up, a severe drop in pH can occur that will be harmful to any fish in the aquarium. Plants are also affected by changes in pH, but not as drastically as fish. Most aquarium plants are happy in water with a pH value between 6.0 and 7.5.

Sudden drop in pH can be life threatening.

How buffering capacity works

Acids

Acids

Fish and plants thrive in a well-buffered tank.

Minor pH fluctations are not a problem.

^ With no carbonates and/or buffering capacity, any acids produced will lower the pH level. This can happen quickly, causing death to fish and damage to plants.

7 Regular water changes help to replenish carbonates, maintaining a good buffering capacity. In a well-buffered aquarium, the pH level will stay relatively constant.

2/A lack of water changes or using water with low hardness (such as R.O. water) without an artificial buffer reduces carbonate levels and pH fluctuations may occur.

Buffer

Buffer

The day-night cycle in the aquarium oxygen Carbon dioxide

Although fish need oxygen, it is best for plants not to boost oxygen levels during the day.

Plant photosynthesis uses up carbon dioxide and produces oxygen.

Plants respire, using up oxygen and producing carbon dioxide.

How Plants Respire

Fish and other animals - Including bacteria - respire, using up oxygen and producing carbon dioxide.

Plants respire, using up oxygen and producing carbon dioxide.

Although fish need oxygen, it is best for plants not to boost oxygen levels during the day.

Fish and other animals - Including bacteria - respire, using up oxygen and producing carbon dioxide.

Plant photosynthesis uses up carbon dioxide and produces oxygen.

NIGHT Plant photosynthesis stops, so carbon dioxide levels rise in the aquarium.

NIGHT Plant photosynthesis stops, so carbon dioxide levels rise in the aquarium.

Photosynthese Aquarium

Plants respire, using up and producing carbon dioxide.

At night, aeration to boost oxygen levels is a good thing.

Aquarium Plant Photosynthesis

Fish and other animals - including bacteria - respire, using up oxygen and producing carbon dioxide.

At night, aeration to boost oxygen levels is a good thing.

Diurnal fluctuations

The combination of continual respiration and photosynthesis during daylight creates a fluctuation throughout the day that affects the oxygen and carbon dioxide levels in the surrounding water. Rising and falling oxygen and carbon dioxide levels have a direct effect on the pH and hardness of the water. These changes in water conditions are called diurnal fluctuations and occur in all natural waters. When there are plants in the aquarium, diurnal fluctuations are increased by the relatively high concentration of plants and small volume of water.

As plants start to receive light in the morning, they begin to photosynthesize and use up carbon dioxide while releasing oxygen. Although the opposite process is also being carried out through respiration, the process of photosynthesis is carried out much more quickly and with a greater quantity of gas exchange. As the plants photosynthesize, carbon dioxide levels in the water begin to drop and the amount of carbonic acid produced also falls. The release of oxygen will also bind organics and minerals, and combined with falling carbonic acids, this causes pH levels to rise (become more alkaline). Once dissolved carbon dioxide is used up, plants begin to find other sources of carbon dioxide, mainly from bicarbonates. Bicarbonates form part of water hardness and as they are used up by plants, the surrounding water will become softer. These two processes create water with a high pH (alkaline) yet with a low hardness.

At night, plants cease to photosynthesize and stop producing oxygen, although they continue to respire. This has the effect of reducing oxygen levels and raising carbon dioxide levels in the water. The dissolved carbon dioxide will bind both with minerals such

Test pH at the end of day/night to record highest/lowest readings.

Living Things Respire

Living organisms respire, producing C02. Plant photosynthesis uses Plants stop photosynthesizing at night but continue to up most of the C02, so carbonic acid cannot be produced at respire, as do fish and bacteria, producing C02. This sufficient levels to keep pH low. Carbonates and minerals bind with creates a steady rise in C02 and carbonic acid is formed, any acids, removing their acidic effect and raising the pH level. causing the pH to drop throughout the night.

as calcium, creating bicarbonates that raise water hardness and buffering levels, and with organics, creating carbonic acid that will lower pH (more acidic). During a 24-hour period these processes have the effect of raising oxygen, hardness, and pH levels during the day, while lowering levels at night.

The same fluctuations occur in the aquarium, although if carbon dioxide is added artificially, the aquarist can control or reduce these fluctuations. Providing plants with an ample supply of carbon dioxide means that they will not need to use up bicarbonates, and fluctuations in water hardness are reduced. However, pH fluctuations will still occur because of the difference in oxygen and carbon dioxide levels during the day and night. Some carbon dioxide systems can be linked to light units and/or timers so that carbon dioxide is only introduced when it is needed. This will help to reduce fluctuations in pH levels.

In most cases, both fish and plants are accustomed to these fluctuations in water quality, although you should regularly test pH and water hardness levels, both in the morning and at night, to ensure that any fluctuations are stable and not too extreme. Changes of more than 1° in pH may cause health problems to some fish. Carbonate hardness should be tested, because a lack of bicarbonates will cause the aquarium buffering capacity to drop, which in turn creates larger fluctuations in pH levels. This is one reason why very soft water often causes problems when aquarium plants and fish are kept together.

Water testing

Ammonia, nitrite, nitrate, pH, and water hardness levels can all be tested using test kits that are easy to use and widely available. Nutrients, oxygen, and carbon dioxide levels are not as easy to test for

Living organisms respire, producing C02. Plant photosynthesis uses Plants stop photosynthesizing at night but continue to up most of the C02, so carbonic acid cannot be produced at respire, as do fish and bacteria, producing C02. This sufficient levels to keep pH low. Carbonates and minerals bind with creates a steady rise in C02 and carbonic acid is formed, any acids, removing their acidic effect and raising the pH level. causing the pH to drop throughout the night.

How pH changes over a 24-hour period

Test pH at the end of day/night to record highest/lowest readings.

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Aquarium and Fish Care Tactics

Aquarium and Fish Care Tactics

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