Pets

Water is an essential constituent of all life forms; to fishes, however, it is environmental as well as metabolic the medium in which they live, just as we live in air. Like us, fishes pass water through their excretory and alimentary tracts; but they also "breathe" it, using their gills (and sometimes other organs) to extract essential oxygen and discharge carbon dioxide. There is also an exchange of metabolic and environmental water by osmosis. We become uncomfortable or ill if we drink polluted water, or if the air we breathe doesn't suit our individual preferences (usually what we are used to) or the general requirements of our species it may be too hot, cold, still, windy, dry, or humid for our liking, too low in oxygen, or polluted with smoke or toxic gases.

Air, however, has a fairly uniform chemical composition throughout the world, so someone from one part of our planet can survive in any other, though he or she may find the local climate unpleasant.

Water, by contrast, is highly variable in its chemistry: it can be fresh, brackish, or saline; hard or soft; acid or alkaline; rich or poor in oxygen; pure or polluted. Unlike us, fishes are restricted in their distributionwe can go anywhere there is air, but not all bodies of water are accessible to all fishes, for reasons of geography (for example a sea fish cannot enter a land-locked lake) and environmental unsuitability. The latter is usually the end-product of the former - geological activity isolates a body of water and its fauna; subsequently there is gradual modification of water parameters (chemistry, temperature, quality) paralleled by adaptation of the fishes to the changing conditions. Their systems, thus specialized, are then often unable to cope with any subsequent change. They may suffer discomfort or poor health, or even die, if the water in which they find themselves which they "drink" and "breathe" and which interacts with their body fluids does not meet their specific requirements especially if the change is abrupt.

We must therefore never assume that water is a uniform element, or that any fish will live happily in what comes out of the tap. The aquarist must be a "water technician", providing the correct environment in terms of chemistry, temperature, oxygen content, movement, and freedom from pollution ("water quality"). There are instruments and test kits for monitoring aquarium water, and a huge variety of equipment for adjusting its chemistry, quality, and other factors, so there is no excuse for hit-and-miss water management.

Water Chemistry
This is the term used by aquarists to describe the combined salinity, hardness, and acidity/alkalinity (pH) of water. For a fish to survive its metabolism must be in tune with these aspects of its environment, and successful adaptation to significant
alterations normally requires changes to be gradual, allowing time for metabolic adjustment. Sudden change can be fatal if a fish's organs cannot cope with the altered environment ("chemical shock"). While some fishes can be adapted to "unnatural" water chemistry, this may prove detrimental in the long term; and the difference between certain environments, for example salt and fresh water, is too great to overcome.
There are two sensible ways of approaching this question of water chemistry:

• You can either keep fishes suited to the water you can provide from the tap,
• Modify your local water to meet the needs of more demanding species.

Modification of water chemistry can be expensive and time-consuming, with the possibility of error, so we suggest that beginners take the former course. We do not recommend the third option of attempting to modify the fishes!

Your dealer should be able to tell you which species are "hardy", and which will not live long in your tap water. Even so, check whether the hardy types are actually found in water similar to yours in the wild if not you may still need to modify it for breeding. Some species occur naturally in several. In nature Dimidiochromis compressiceps (the Malawian eyebiter) feeds on the fry of other species and is reputed to eat the eyes of adults. In captivity it is rather timid, and does not behave "antisocially" if well fed. It should, however, be kept only with other Malawi cichlids, and like them requires moderately hard, alkaline, well-oxygenated, water. Different bodies of water sometimes offering quite diverse environments. Without specific data on origin the best approach is to create average conditions for the species, modifying these slowly if the fish appears unhappy.

Sudden increases in hardness or dramatic alterations in pH are the changes most likely to have dire effects; even natural water chemistry may prove harmful if the fishes' systems have adjusted to different conditions. Local shops usually use tap water (except for marines and some delicate freshwater species ? do check in each case), so it may be best to do likewise initially and gradually adjust water chemistry after introducing the fishes. Later on you may wish to buy additional fishes, possibly accustomed to different conditions to those now prevailing in your aquarium. In such cases set up a temporary tank with conditions suited to the new arrivals, then adjust water chemistry gradually to match your main aquarium.

You may be told that chemical shock can be minimized by mixing small amounts of aquarium water with that in the bag prior to releasing fishes. That is rubbish - the necessary metabolic adjustment takes days or weeks, not minutes.

Salinity
This is the measure of common salt (sodium chloride, NaCI) content, and is normally applied only to salt and brackish water (fresh water, by definition, does not contain measurable quantities of NaCI). It is measured using a hydrometer. Nowadays, because of coastal pollution, water for the marine or brackish aquarium is normally "created" (rather than collected), using tap water and special "marine salts" containing not only sodium chloride but also desirable trace elements. Instructions are normally provided, but the salinity of the mix should always be checked. (It is important to remember never to use "domestic" salt, which may contain additives toxic to fishes.)

Hardness
Hardness is the measure of dissolved mineral salts (mainly chlorides, bicarbonates, carbonates, and sulphates of calcium, sodium, magnesium, and potassium); the harder the water the more salts it contains. It is generally expressed in terms of calcium carbonate (CaCO3) content, measured in degrees (dH) or parts per million (ppm) using a special test kit. Care is needed with regard to "degrees of hardness", the definition of which varies from country to country and test kit to test kit, depending on origin.

Water becomes hard by dissolving soluble salts from the rocks or soil over or through which it flows. Some rocks, for example slate, granite, and gneiss, contain little or no soluble material and have a negligible effect, while others, notably limestones, are quite the opposite. Rocks and other "hard" decor in the aquarium may affect water chemistry: corals and shells are largely calcium carbonate, and gravel often contains fragments of limestone or shell. Hardness-free decor is a prerequisite of the soft-water aquarium.It is easy to harden soft water with lime rich decor or the special salt mixes (not marine salt) available for simulating conditions in east African lakes, and, as luck would have it, fishes from hard water seem not to suffer any ill effects from softer than natural conditions (but see pH, below). Unfortunately the reverse does not apply: reducing hardness is troublesome, and soft water fishes often fail to thrive in hard conditions.

Softening Water
There are various methods of softening water:

1 By boiling, which removes some, but not all, of the dissolved salts.
2 By dilution with rain water. This is the cheapest method, the only outlay being suitable containers, made of non-toxic material, for collecting and storing water. Roofs, gutters, and down pipes must be as clean as possible, and avoid cemented roofs as cement is powdered limestone. Water collected close to, or downwind of, industrial areas may be polluted. Collect only during prolonged downpours, and wait a few minutes while dust and any other rubbish is washed away. It is advisable to strain the water through filter floss straight away to remove any stray detritus. Rain water may carry the risk of pollution, but so may tap water
3 By dilution with artificially softened water.
This may be:
a) distilled;
b) softened using an ion exchange resin (use only resins sold for aquarium use). This may affect pH, and, as it exchanges calcium ions for (usually) sodium ions, the result may be soft but still mineral-rich (and unsuitable for fishes from mineral-poor waters);
c) processed by a reverse osmosis unit, available from aquatic retailers (but expensive). This removes all minerals but is wasteful ? some 45.5 litres (10 gallons) of tap water are needed to produce 4.5 litres (1 gallon) of mineral-free water.

The collected or treated water can be used "neat" to create very soft conditions. Distilled and reverse-osmosis water should never be used "neat"; not, as often stated, because they contain no minerals, but because both processes remove free oxygen so there is nothing to "breathe". Aerate thoroughly before use to rectify this problem.
You may come across the following additional terms: "Temporary hardness" is that which can be removed by boiling, while "permanent hardness" is that which cannot. "Carbonate hardness" (KH) is that contributed by (bi)carbonates, but not other salts such as sulphates and chlorides. "General hardness" (GH) includes all dissolved salts, and is sometimes referred to as "total hardness" or "total dissolved salts" (TDS). Scientists often measure mineral content in terms not of hardness but of electrical conductivity, the units employed being micro-siemens (AS).

The pH scale is used to indicate the .acidity or alkalinity of a substance; it runs from 0 to 14, 0 being the extreme of acidity 14 that of alkalinity, and 7 neutral. Most fishes come from waters with a pH between 5.5 and 9.0, although there are outliers at either end of the scale. It is vital to remember that the scale is logarithmic ? each step up or down from neutral is 10 times the previous one: pH 4 is 10 times more acid than pH 5, and 100 times more acid than pH 6. Apparently small variations can thus have dramatic effects on fishes.

Luckily the scale is the universally accepted method of measuring acidity/alkalinity, so there is no problem with different units as with hardness. Special test kits are available and affluent aquarists may wish to buy electronic pH meters.
The pH of water is affected by substances dissolved in it. The salts which harden water usually also render it alkaline; soft water, by contrast, is often slightly acid, because rain reacts with atmospheric carbon dioxide to form dilute carbonic acid. Decaying organic material, such as is found in peat bogs and forests, acidifies water flowing through such areas.

There is little point in trying to acidify aquarium water which is being constantly buffered back to neutral or alkaline by dissolved salts derived from tap water or the decor. First minimize hardness, otherwise you are wasting your time. Soft water is easily acidified using peat filtration (see below). Loose peat will "migrate" and is best placed in a nylon bag (a stocking will do), and the whole rinsed to remove tiny particles. Peat is fairly quickly "exhausted" and needs renewing at intervals established by monitoring pH.
Water can be made alkaline by using calciferous decor or by filtering over coral, crushed shell, or limestone chips. Such material should always be included in systems for fishes which cannot tolerate acid conditions, to act as a buffer against the acidifying effects of metabolic byproducts.

These methods are gradual in effect; to avoid "pH shock" when you change part of the aquarium water you may need to adjust the pH of the "new" water rapidly before use (though in practice partial water changes with neutral water rarely have any ill effect). If you use a proprietary "pH adjuster" follow the instructions to the letter ? failure to do so may prove fatal for the fishes. We prefer to prepare new water in advance (leaving it to stand over peat or calciferous material), or to use bicarbonate of soda (NaHCO3) to raise pH, or peat extract (made by boiling peat) to lower it. Dosage must be established initially by adding small amounts to the new water and measuring the pH. Always treat the water before adding it to the aquarium.
Water chemistry is in fact far more complex than we have intimated, because mineral composition (the salts contributing to the hardness) varies considerably from area to area. There is, however, rarely any need to simulate the exact formulation, as fishes are able to extract the amount of each vital element they actually require.

Water Quality
Water quality is equally as important as chemistry. Most of the complexities of the latter can be avoided by keeping fishes suited to local water, but providing and maintaining good water quality is a continuing process. This falls into two parts: ensuring no harmful chemicals enter the aquarium from outside; and dealing with waste products produced by its occupants. Many fishes come from virtually unpolluted water and are highly sensitive to any contaminants. Some are more tolerant, but it is nevertheless unwise to provide less than optimal water quality in captivity ? the sheer volume of natural waters acts as a safety net, whereas any problem can rapidly escalate in the restricted capacity of the aquarium.

All equipment and decor must be non-toxic -where possible use items intended specifically for aquarium use. "Non-aquatic" plastics should ideally be "food quality"; avoid coloured types, especially those with a nasty taste. Metals may corrode (especially in salt water), producing toxic salts, so use only those metal items designed for aquarium use (for example aluminium hoods) and always check suitability for marine aquaria.

Rocks should not (unintentionally) affect the water, but beware of coloured crystals which may be poisonous. Garden items (such as flowerpots and stones) may be contaminated with pesticides or fertilizers. Wood (for example hoods) may leach tannins, or worse, preservatives, unless coated with polyurethane varnish. Insecticide aerosols, spray polishes, paint fumes, and other domestic chemicals can poison fishes. A definitive list is impossible, so always be on your guard.

As if this were not enough, the water from your tap may contain invisible nasty surprises. Water that has stood in metal pipes may be tainted with metallic oxide. This contamination is normally slight but can accumulate in the aquarium, so run the tap for a while before using any water. Never use water from a copper hot-water cylinder.

Water companies are required to provide water "of potable quality". This does not always equate with aquarium quality, as chemical treatments and pollution levels deemed harmless to humans can be lethal to fishes. The commonest additive is chlorine gas, highly toxic to fishes but easily dealt with: if water is left to stand for 24 hours the gas will disperse into the air. The process can be speeded up by aeration, and if chlorine content is low (the gas can't be smelt), it is often sufficient to run the tap hard into a bucket.

Some water companies now use an alternative, far more toxic, purification agent, chloramine, which does not disperse naturally. Water conditioners are available (from your local dealer) to neutralize this chemical, as well as chlorine. Ask your water company if they use chloramine or intend to do so, and ask to be warned whenever they intend to flush the mains to eliminate aquatic invertebrates, as the DDT used is toxic to fishes. Be friendly and polite - their only obligation is to provide drinkable water. Help with your fishes is voluntary.The main disadvantage is that when the system eventually becomes clogged cleaning involves a major upheaval.

A reverse-flow UG system minimizes this problem by using an external canister filter as a mechanical pre-filter, the outlet being attached to the UG uplift so that water is pumped up through the substrate. This unfortunately also negates the advantage of UG - the system inlet is now that of the pre-filter, which is also probably the main site of bacterial activity! Reverse-flow systems create no surface turbulence and this may result in oxygen depletion unless the aquarium is aerated independently of the filtration system.

Tap water may contain nitrates and phosphates (the result of agricultural fertilizers leaching into rivers and aquifers, or of incomplete "purification" during recycling), especially when water levels are low and pollutant concentrations correspondingly high; fortunate the aquarist whose tap water originates from a moorland reservoir or other uncontaminated source. Nitrate test kits are available from dealers. Nitrates should be removed from water intended for the aquarium reverse osmosis, or a special filter connected to the tap.

The Nitrogen Cycle
However good your initial water quality, it will deteriorate when fishes are introduced. Fishes excrete wastes, plants lose leaves, and inevitably there will be particles of food uneaten. In both nature and the aquarium such detritus is broken down by bacteria during a series of processes termed the nitrogen cycle. The first stage in this cycle is highly toxic ammonia (and its compounds), excreted by fishes and produced by the decomposition of organic matter; this is rapidly converted to nitrites (still dangerously toxic), which are in turn processed into nitrates. These are relatively harmless, though sudden or long-term exposure to high concentrations can be harmful.

Sponge Filters: A sponge filter consists of a perforated plastic tube fitted with a cylindrical sponge. Air is passed through the tube, drawing water through the sponge. These filters act mechanically and biologically; they are best suited to aquaria with low filtration needs.

Protein Skimmers: Protein skimmers, essential in the marine aquarium, utilize a process known as "air stripping". Proteins and other organics adhere to air bubbles, forming a foam which rises to the top of the unit to be collected in a removable container which is emptied at least once a day. They do not work in fresh water.

Optimizing Water Quality
The amount and type of filtration required depends on the nature of the individual aquarium. Biological efficiency is a function of bacterial population size, in turn dependent on available colonizable area (filter capacity) and oxygen supply ? not, as many aquarists assume, purely on turnover rate. In choosing a filtration system take into consideration tank size, probable metabolic loading (number, sizes, and feeding habits of the fishes relative to water volume), and water movement requirements (of the fishes), in order to decide what filter type, capacity, and turnover rate suit your specific circumstances. Expert advice (for example from your dealer) can be invaluable. Filter efficiency can be monitored using the kits available for measuring ammonia, nitrites, and nitrates.
Although biological filtration will deal with ammonia and nitrites, it will not eliminate nitrates, and without additional action a gradual build-up of these is inevitable, even if some are utilized by plants. Although nitrates are relatively harmless, long-term exposure to high concentrations may shorten lifespan and reduce resistance to disease. Sudden exposure to high nitrate levels is often fatal for example if new fishes, unaccustomed to high levels, are introduced. Far too often the retailer is blamed for selling poor-quality fishes!

The most effective way of reducing nitrates (you cannot eliminate them altogether in a functioning system) is to replace part of the aquarium water regularly; how much and how often depends on the individual tank, but 20 per cent weekly is a good starting point. Monitoring with a test kit will indicate whether the routine needs to be modified. It is inadvisable to change more than a third of the water at a time, and replacement water should be detoxified (if necessary) and be of the correct chemistry and temperature. Although chemical media are available for removing nitrates, fresh water is preferable because it has the added benefit of stimulating fishes and replenishing minerals exhausted by them. Just topping up to replace water lost by evaporation does not constitute a partial water change, because any chemicals (whether organic - for example nitrates - or inorganic) are left behind during evaporation and so remain in the water.

Other Aspects of Water Management
Fishes have evolved to function at particular temperature ranges just as they have adapted to local water chemistries. In nature, variation within a species' acceptable range is normally gradual; sudden changes (as inflicted by careless aquarists) may be harmful, with a rapid drop in temperature more serious than a rise. There are species-dependent upper and lower limits above and below which metabolic failure (and death) are probable, but most species will continue to function (at least for a while) at temperatures slightly outside their optimal range.

They may be sluggish if the temperature is abnormally low (never skimp on heating), and suffer respiratory distress if it is higher than normal: increased temperature results in increased metabolic rate and hence oxygen requirement, but there is a concomitant decrease in the oxygen content of the water ? so the gills need to work harder on both counts. Oxygen requirements themselves vary from species to species, yet again as a function of the natural habitat. The more turbulent the water the more rapidly it can absorb oxygen from the atmosphere and the greater its oxygen content is likely to be. The reasons for this are two-fold: first, oxygen is absorbed only at the interface between air and water (its surface), which increases in area when in motion; second, water movement speeds up circulation of the oxygen, which, in completely still water, would spread from the surface only very slowly, by diffusion.

Large bodies of water (seas, large lakes) are subject to, massive water movements (tides and storms) which result in high oxygen concentrations; not surprisingly the resident fishes have adapted to these levels, and, if deprived of them, may die by gradual suffocation. Some species from fast-flowing rivers may be similarly affected. At the other end of the scale there are bodies of water which contain very little oxygen, yet fishes nevertheless survive there, often because they have evolved the ability to supplement their air supply directly from the atmosphere.

It is vital to ensure suitable oxygen levels in the aquarium, using artificial aeration if necessary. The return from the filter may supply the necessary turbulence, or an airpump and aeration device (an air-stone or other diffuser) can be used. Most of the uptake of oxygen results not from the rising stream of bubbles but from the turbulence created as these break the surface. Filtration and aeration also serve to circulate oxygen around the aquarium. Do, however, beware of creating unnecessary turbulence in tanks housing fishes from still waters (generally with low oxygen content) as their bodies and finnage are usually adapted to conditions in their natural habitat, and they may find it hard work to swim in a miniature jacuzzi; the resulting long term stress may prove harmful.

To conclude this chapter, a few additional do's and don'ts. Always follow manufacturers' instructions when using chemicals, test kits, and equipment. Never guess quantities when adding chemicals - measure accurately and test the result every time. Don't however, take test results as gospel if they don't make sense (for example a zero nitrate reading) ? test kits often have a shelf life, and occasionally defective batches occur. If a test result differs dramatically from what appears reasonable, test again, with another kit if necessary. Finally, do always remember the immense importance of providing water which is correct in every respect, and if in doubt, always imitate nature.

Although the nitrogen cycle will operate in any mature aquarium, fish population density is generally higher than in a comparable volume of water in nature, so the system is unbalanced; a tank may look clean but have high levels of ammonia or nitrite. Action is necessary to redress the balance and avoid such problems. The process normally used is filtration, during which the aquarium water is passed through one or more materials (filter media) to remove wastes. There are three main types of filtration ? mechanical, chemical, and biological ? and aquarium systems are usually a combination of at least two of these.

Types of Filtration
Mechanical Filtration: During mechanical filtration solids are trapped by the filter; they are, however, still part of the aquarium system until the medium is replaced or cleaned, just as dust swept under the carpet is still in the house! The commonest media used are filter floss, plastic foam, and gravel/sand.
Chemical Filtration: This process uses media which alter the chemical composition of the water, for example the alteration of pH using peat or lime-rich material, reduction of hardness by ion-exchange resins, and removal of metabolic products by activated carbon or zeolite (which remove carbon dioxide and ammonia respectively). Chemical media also trap solids mechanically. Biological Filtration: Biological filtration involves enhancing natural populations of the bacteria which operate the nitrogen cycle by providing the conditions they require ? surfaces to colonize, supplies of wastes to process, and, for those which convert nitrites to nitrates, a constant supply of oxygen. The filter medium offers living space, and the flow of water through the filter ensures a constant supply of wastes and oxygen. Biological filtration takes place in any mechanical or chemical filter which has been left undisturbed long enough to develop a bacterial population, and the media used in biological filters also have a mechanical (and sometimes chemical) effect. As well as those already mentioned there are plastic, ceramic, and glass media, all of which maximize the surface area available for colonization. Efficient biological filtration is the key to maintaining water quality on a day-to-day basis.

The nitrogen cycle must be considered when planning and maintaining a filtration system, as whether you want biological filtration or not you are going to get it! It takes about two weeks for the nitrogen cycle to become properly functional in a new system (aquarium and filter(s)); fishes cannot be introduced until after this maturation period because of ammonia/nitrate toxicity. If the established nitrogen cycle is subsequently interrupted there will again be a risk of toxicity. This commonly happens when "dirty" filters are cleaned because they are considered to be unhygienic and life-threatening; in fact most of the "dirt" in a mature filter is the inert (and harmless) residue left by bacterial processing. Removing it does nothing to improve hygiene, but the accompanying elimination of the established bacterial population can wreak havoc. It is, however, sometimes necessary to clean filters if clogging by inert matter is impeding flow, or if chemical media are exhausted. Only part (50 per cent maximum) of the filter contents should be cleaned or replaced; this will leave an adequate residual bacterial population, but feeding should nevertheless be reduced for a few days to lighten the load on the biological system while it regenerates to full strength.

Canister Filters: These are self-contained units with a container (the filter chamber) for media and an electric pump to circulate water. They may be external, with inlet and outlet pipes from and to the aquarium, or internal, with slits to allow water into the filter and an outlet from the pump. They combine mechanical and biological filtration, with chemical optional. Special external filters using diatomaceous earth optimize water clarity by mechanically removing particles but are expensive to run and need frequent maintenance as they clog rapidly.

Canister filters are mechanical and biological, sometimes chemical, in operation. Water is siphoned out of the aquarium into the filter canister, then pumped up through the filter media and back to the aquarium, in this case via a spray bar.

Undergravel (UG) Filters: UG filters consist of a plastic plate positioned between the aquarium bottom and the substrate, with one or more uplift pipes. Water is drawn down through the substrate and returned via the uplift(s). UG filters can be powered by: a) the airlift principle (rising bubbles of air draw water with them), an airline being inserted in the uplift tube; b) powerheads, electric pumps which fit on to the uplift tubes; or c) an external canister filter with its inlet tube inserted in the uplift. The substrate, which should be 5-7.5 cm (2-3 inches) deep for maximum effectiveness, acts as the filter medium, and its action is both mechanical and biological, sometimes chemical. The advantages of undergravel filtration are that the "inlet" is the entire aquarium bottom so wastes cannot escape processing, and the large amount of
filter medium available for bacterial colonization.
Trickle Filters: These consist of one or more trays with perforated bottoms, part-filled with filter media, stacked above the aquarium, and used in conjunction with an external canister filter, whose return is sprayed on to the (top) tray and trickles back into the tank via the perforations. The water is thus exposed to air, optimizing its oxygen uptake and hence bacterial activity. A further advantage is that its capacity (the volume of media) can be increased by means of additional trays without the need to increase turnover (water flow rate). Trickle filters may alternatively be situated beneath the aquarium, with the water being siphoned into the filter and pumped back. Trickle filters are usually sited on top of the aquarium and fed by the return from a canister filter (spray bar). Water and filter media are exposed to atmospheric oxygen, making for excellent biological efficiency.
Box Filters: Box filters may be internal or external and are driven by the airlift principle. They have, however, largely been superseded by more complex systems, but the internal type is still useful for small tanks, tanks with minimal loading, and supplementary chemical filtration.

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