Wednesday, February 25, 2015

Aquarium : Fresh Water Temperature, Characteristics,Scientific Values and information

fresh water characteristics

Water, a haven for life:

Without water, there would be no life on our planet. Excessively pure water, however, does not enhance the development of living organisms.

As it is the elements contained within water that make this possible. Getting fish for plants to live and reproduce in an aquarium therefore requires some basic knowledge of the characteristics of water, which, although a constant presence in our daily existence, is often little understood as an environment that supports living organisms.


What is Fresh Water?

Fresh water is also known as Continental water, a more accurate term from the scientific point of view. Continental water accounts for only 2.6% of the Earth's water, the rest being made up of seas and oceans. Of this volume, 98% consists of sterile water, in the form of glaciers and underground water, leaving only the water of rivers, lakes, and ponds as shelter for living organisms- barely 2% of the total volume of Continental water.

Fresh Water Temperature

 An important parameter for aquatic life, the temperature regulates the growth of animals and plants and exerts an influence not only on oxygen levels but also on many other factors.

Whereas mammals have a regulated and practically stable internal temperature, that of fish and other aquarium creatures varies according to the temperature of the water around them.

They can survive only at certain temperatures and some species are more sensitive than others to variations in this parameter. The temperatures of fresh tropical waters, ranging from 20 to 30°C, are characterized by less significant variations than those found in temperate regions.

In some places the shade provided by the tropical forest cools the water, while in calm water the temperature goes up under the direct influence of the sunlight.

The mean temperature most often recommended for aquariums is 25°C, and variations of 1 or 2° are of little consequence. Fish are even capable of withstanding even more significant variations for brief periods (under 24 hours).

On the other hand, their metabolism (i.e. their general bodily functioning) is in danger of serious disturbance over any longer periods, and sooner or later they may die. It must also be noted that excessively low temperatures sometimes favor the development of certain diseases.

Fresh Water Oxygen and Carbon  Dioxide

Since air contains around 20% oxygen, even the most oxygenated water rarely contains more than 1% dissolved oxygen. Fish have special organs - branchiae - which allow them to extract most of this (see Anatomy and Biology.

Oxygen contributes, in addition, to the respiration not only of plants but also of organisms which are invisible to the naked eye and often forgot-ten: the bacteria. The latter transform the organic matter emitted from living beings (excreta and various other residues), and these chemical reactions similarly require oxygen.

The oxygen in water comes from the dissolution of the oxygen in the air, a process enhanced by movements in the water produced by wind, currents, or downward flow. The more water is stirred, the more it is oxygenated. Plants also provide oxygen, which they produce through photosynthesis, although this process occurs only by day.

The maximum amount of oxygen that water can contain is determined by its temperature: the higher this is, the less oxygen the water can contain (at 25°C there is 18% less oxygen than at 15°C). Oxygen is measured in mg/liter, and its control is quite a complicated matter. The most turbulent, and therefore the most oxygenated, water contains 8-10 mg/liter, while the most deficient water sometimes has less than 2 mg/liter.

oxygen and carbon dioxide production and consumption

The oxygen content in an aquarium is usually at its maximum, providing the recommendations for stirring the water are followed. The rare problems which do occur are the result of negligence as regards the overall balance of the aquarium (overpopulation of fish, small number of plants), or non-functioning of equipment due to forgetfulness, breakdown, or a power cut. Carbon dioxide derives from the respiration of fish, plants, and bacteria.

Stirring the water enhances its oxygenation, thereby reducing the levels of carbon dioxide in the water, and passing it into the atmosphere. Carbon dioxide is quite rare in an aquarium, and this can, to some extent, prove prejudicial to plants, as they absorb it by day through photosynthesis to extract the carbon they need to grow.
It is therefore vital to establish a permanent equilibrium between oxygen, carbon dioxide, plants, and fish, although this balance changes at night, when plants stop producing oxygen. Carbon dioxide is also one of the main factors affecting the pH.

Fresh Water PH Values

The pH measures the acidity or alkalinity of water, with the value 7 representing neutrality. Below this level the water is acid, and above it the water is alkaline (or basic). Categorizing water as acid does not mean that it contains dangerous acids.

In forest streams and rivers the water accumulates with acid organic fluid (humic acid) derived from the decomposition of plants (humus), producing an amber yellow color. Generally speaking, aquatic life can exist only between pH 5 and 9.

These extreme values are rarely found in an aquarium, where the pH ranges from 6 to 8 according to the type of water, and usually lies between 6.5 and 7.5. In aquariums, the term acid water corresponds to a pH between 6 and 6.8, while alkaline water refers to one between 7.2 and 8, and a pH between 6.8 and 7.2 is considered neutral.

Variations in pH are mainly the result of biological activity: the carbon dioxide produced by living beings acidifies the water at night and the pH goes down slightly. Once the carbon dioxide has been absorbed by the plants during the day the pH goes up again. Although slight variations are therefore normal, more extreme changes can be a warning signal.

The pH is a good indicator of an aquarium's equilibrium, and it should therefore be measured regularly. A colored marker dipped into a sample of water is used to compare the color obtained with the scale provided. Electronic meters are also now available for testing pH values.

Adjusting the pH 

The pH of domestic water may not always be particularly suited to the fish you have chosen. Furthermore, when an aquarium is in use the pH can rise and fall, slowly but very regularly.

There are some aquarium products on the market that enable adjustments to be made to the pH, but there are other ways of modifying it.

• If the pH is too high - the water can be diluted with another more acid water; - the stirring of the water can be reduced. Carbon dioxide is eliminated less quickly and remains in the water to acidify it. Be careful, because decreasing the stirring also lowers the oxygenation; - the water from the aquarium can be filtered over peat, which will release certain acids. The amount of peat needed to maintain a specific pH value must be found through trial and error, with regular measurements of the pH.

• If the pH is too low - the water can be diluted with another more alkaline, and generally harder water (see Hardness, below); - the agitation of the water can be increased, enhancing the elimination of the carbon dioxide dissolved in the water and therefore lifting the pH; - the water can be filtered over calcareous material, rock, or oyster shells broken into little pieces. In this case, the hardness also increases.

Fresh Water Hardness

fresh water hardness
There are kits on the market that offer
even the novice aquarist the panoply of
tests required to control the majority of
the main parameters for water.
The hardness of water refers to the combination of substances based on calcium (Ca) and magnesium (Mg) that are contained in it. The main substances, known as salts, are carbonates, bicarbonates and sulfates.

Water with zero hardness does not contain any of these salts; this is the case with distilled water. The water in some areas can be particularly hard, mainly due to the presence of limestone (or calcium carbonate).

The hardness of water really depends on the land through which it has passed: the more calcium and magnesium the rocks contain, the harder the water.

The effects of this can be seen in domestic use: a washing machine, for example, will require more detergent. Above certain limits of hardness water is unfit for human consumption or any other use. Water with a low degree of hardness, i.e. containing few calcium and magnesium salts, is considered soft. Water with a high degree of hardness is classified as hard.

Check this Infographic: The hardness of water

Fresh Water Food Chains

In nature Life in water, as on land, is not possible without light. Vegetation (microscopic plankton or plants) absorbs it with carbon dioxide (CO2) and uses the mineral salts, which act as nutrients. This vegetation serves as food for herbivorous or omnivorous fish, which in their turn provide nutrition for carnivorous fish.

From this point, the next link in the chain can be aquatic (dolphin, shark), terrestrial (man), or aerial (bird). When aquatic organisms die, they fall to the bed. Their bodies are degraded by the action of bacteria, the material is recycled into mineral salts, and so the chain comes full circle. (While they are alive, it is their excreta that are recycled.)

fresh water food chains

Fresh Water Peat

Peat derives from the decomposition of vegetation in an acid environment lacking in oxygen. This
fresh water peat Hemigrammus erythrozonus
process, which lasts several centuries, gives rise to a peat bog from which compact, fibrous peat can be extracted. It endows water with both a yellow amber color and acidity, which gives it slightly antiseptic properties. This means that some diseases are less common in acid water.

The use of horticultural peat, which often has been enriched with various products, must be avoided in favor of the peat for aquarium use that is commercially available. Boil it for around 15 minutes before use.

In the Amazon region of South America, the color of the water ranges from amber yellow to brown, due to the leaves and branches floating in it. In an aquarium, peat can be used in the filtering equipment to reproduce the characteristics of this type of water (low hardness, pH under 7, coloring).

The hardness of water is expressed in German degrees (°GH or °DH), not to be confused with Celsius degrees (°C) for temperature: 1°GH is equivalent to 17.9 mg
Ca/liter, or 17.9 parts per million (ppm). The term most often used to classify hardness is general hardness (GH),although total hardness (TH) can also be used.

There are three main categories of water in fishkeeping: - soft water, which is generally acid, at 3°GH or 50 ppm; - medium water, which is neutral or slightly alkaline, at 6°GH or 100 ppm; - hard water, which is highly alkaline, at 12°GH or 200 ppm. We will go on to discover that some fish families can adapt only to certain types of water.

Measuring GH of Fresh Water

A colored indicator is used: the number of drops needed to obtain a change in color indicates the degree of hardness. It should be noted that the degrees of hardness used in analysis kits may vary according to the country in which it was manufactured; in some cases French degrees are used.

These can be converted as follows:

• How can the degree used by a manufacturer in a product be identified?
To confuse matters further, you may also come across Clark in older books on fishkeeping. The old-fashioned Clark system for hardness was somewhat laborious, being based on measurement of the foam created by a soap solution, and has now become obsolete. If you have any doubts about the units used by the manufacturer of an analysis kit, just measure a GH you already know, such as that of bottled water.

The relationship between GH and CH 

Capeta tetrazona
A Capeta
tetrazona (here
the golden variety)
prefers soft to
water, especially
for reproduction.
We have already seen that significant changes in the pH are prejudicial to aquaticlife, especially if they occur too abruptly. To compensate for this, nature has provided a screening device, the CH (carbonate hardness, i.e. the hardness due to calcium and magnesium carbonates and bicarbonates). The higher this is, the less the risk of any major variations in the pH. and vice versa.

This phenomenon, known as buffering, can therefore only occur in acid fresh water. There is a relationship between the CH and the general hardness: the closer the CH value comes to the GH value, the more balanced the water. If the CH is less than 75% of the GH, you are likely to encounter a problem, and it is therefore not advisable to use water with these characteristics in an aquarium.

Modifying the hardness of fresh water 

Sometimes the water available presents a hardness value inappropriate for its intended use in an aquarium. In most cases, the water will be a little too hard, and so the GH must be brought down for use in a mixed aquarium or a rearing tank.

In other, less common cases, the water can be slightly too soft, and so the GH needs to be raised. • Reducing the GH Water with a low hardness value can be mixed with water that is too hard. There are several alternative sources of water - rain water; - spring and well water; - defrosting water from a refrigerator; - water from melted snow; - distilled water, available in bottles; - some brands of mineral water; - natural flowing fresh water.

The volume of water that can be obtained, and its price, obviously depend on which of these sources is used. Filling a tank with a capacity of several hundred liters with water of a precise hardness can sometimes be a laborious process. A final piece of advice: avoid using water from a domestic softener, as the calcium salts are replaced by other salts.

Osmosed water is an attractive option, but the equipment represents a substantial investment. • Increasing the GH The water in question can be diluted with harder natural water, generally easier to find than soft water, or put some calcareous rocks in the aquarium, regularly monitoring the GH, or filter the water over oyster shells crushed into tiny pieces. Any modification in the hardness of water is matched by a modification in the pH: increasing the hardness of the water also increases its pH, and vice versa.

Obtaining water with a precise hardness Let us suppose we have two types of water, one hard and one soft, with which to "manufacture" an intermediate water: - water A, with a GH of 9°GH; - water B, with a GH of 3°GH; - target water, with a GH of 5°GH. Calculations: GH water A - GH target water = 9 - 5 = 4. GH target water - GH water B = 5 - 3 = 2.

The combination of 4 liters of water B and 2 liters of water A results in 6 liters at 5°GH. Filling a 180 liter tank will require 180 (6 x 30 times this mixture, i.e. 60 liters of water A and 120 liters of water B). Another example with the same water: filling the same tank with water at 7°GH will require 120 liters of water A and 60 liters of water B.

Fresh Water Turbidity

The turbidity of water refers to the presence of suspended matter - either living organisms forming plankton (rare in an aquarium) or inert matter, such as animal or vegetable remains or particles of sediment, particularly mud. The size of this suspended matter ranges from a few thousandths of a millimeter to several millimeters.

In calm, unstirred water it forms sediment at a speed in proportion to its weight. In running or turbulent water, some of the matter remains permanently suspended, giving rise to more pronounced turbidity. In aquariums, where the water is always in motion, systems of varying degrees of sophistication  allow fishkeepers keep their water clear.

The effects of this are entirely positive: - the visual appearance is improved; - the light required by the plants penetrates the water and reaches them more easily; - there is less risk of disease, particularly in the fishes' branchiae; - there is little sedimentation on the base of the tank, reducing both the possibility of any warping due to excessive weight and the decomposition of organic matter.


 Nitrogen (N) is one of the components of certain substances, largely derived from the excretion of fish, that are dissolved in water. These substances, of varying structural complexity, are quickly converted into ammonia (NH3 or NH4+), which is highly toxic for animals.

At this point oxygen and bacteria intervene to convert the ammonia into nitrites (NO2-), which are also very toxic. Other bacteria, still accompanied by oxygen, transform them in their turn into nitrates (NO3-), slightly toxic for fish but which can be used by plants as nutrients. These transformations, taken as a whole, are referred to as the nitrogen cycle. In nature, land-based elements can also participate (see diagram). As plants are at the base of the food chain, they also take part in the nitrogen cycle.

In an aquarium, the situation is different. Some fish partly feed on plants, but most of them are fed by the aquarist; sometimes there is a surplus of foodstuffs and the nitrogen cycle is altered as a result. It is very important to respect the equilibrium of this cycle. That is why you should not keep too many fish and you should not overfeed them.

It is also a good idea to provide the aquarium with a sufficient amount of vegetation, and to enhance the development of bacteria, while ensuring that the water is well aerated. Partial and regular water changes make it possible to eliminate surplus foodstuffs, various types of organic matter, and any nitrates that have not been used by the plants. A biological filter enhances the development of the nitrogen cycle.

Bacteria in the nitrogen cycle

Rarely found in open water (around 1% of the total count), bacteria colonize essentially the floor and the decor. They feed on nitrogenous compounds in the water, extracting the oxygen from them.When an aquarium is brought into use, bacterial colonization of the environment is a slow process, and so it is advisable not to introduce the selected fish until 2 or 3 weeks have elapsed.

The toxicity of nitrogenous compounds 

The concentration of nitrogenous compounds in an aquarium is higher than in a balanced natural setting, and there are some limits which must not be exceeded (see table above). Ammonia is found in two different forms in water, and the sum of the two must not be more than 0.4 mg/liter. Dissolved NH3 ammonia gas is the most dangerous, although it only appears above a pH of 7 and rarely exceeds 10% of the total ammonia. The more common ionized NH4+ form is slightly less dangerous.


No nitrogenous substance should pass the threshold limit in a well-balanced aquarium. As ammonia and nitrates are more difficult to assess, it is the nitrites that must be analyzed regularly. There is a colored marker commercially available, which gives a stronger color according to the amount of nitrites present.

If the latter are too abundant: - either there is a general imbalance (too many fish, too much food in the water) which entails a high production of ammonia and, therefore, nitrites; - or there is a problem connected with the transformation of nitrites into nitrates, often a lack of the oxygen required by bacteria. The level of nitrites, like the pH level discussed above, is a good indicator of the equilibrium of an aquarium, and it is therefore important to measure it regularly.


A great many other substances are to be found dissolved in water. Their content is generally low and does not pose any problems, and some of them, such as micronutrients, are even very beneficial. This term covers a variety of elements including vitamins and metals, which in tiny quantities are indispensable to life.

Iron, for example, plays a role in the composition of hemoglobin, the red blood cells which transport the oxygen taken in by the branchiae. It also participates in the photosynthesis of plants, which have a tendency to turn yellow if there is an iron deficiency.

Manganese is equally important, as it is one of the components of chlorophyll, the green pigment in plants that allows them to absorb light and develop. There are, of course, other metals that are also naturally present in water, but their concentration hardly ever exceeds a few thousandths of a mg/liter, and some, such as copper, become toxic if it goes beyond this limit.

Origin and quality of fresh water used in aquariums The simplest and cheapest means of obtaining water is turning on a faucet, but there are other possibilities, especially when it comes to obtaining natural water.

• Domestic water As long as water is drinkable, there is no reason why it is not suitable for fish. In some regions the water is sometimes too hard (general hardness above 11°GH), and so the option of mixing it with softer water must be considered. Domestic water must never be introduced in large quantities into an aquarium which already contains fish. It is also advisable to let it settle for 24 hours to eliminate any excess of gas (caused by the pressure). When filling a tank before putting it into operation, this step is not compulsory, as it will not be housing fish immediately. • Natural water Natural water close to home usually shares many of the characteristics of domestic water, as it makes up a large part of the public water supply. However, it should be possible to find water with different characteristics not too far away.

• Spring water This is the most desirable water, as it is the purest, with no suspended material, little or no organic matter and a high bacteriological quality. • Well water This is of a similarly good quality, although it sometimes contains an excess of gas. It can occasionally be slightly ferruginous (containing iron), which favors the growth of plants.

Optimum Characteristics of fresh water  suitable for aquariums


ParametersOptimum characteristicsObservations
ColorColorlessYellow-colored water contains organic matter.
TurbidityNoneThe water must be limpid and crystal-clear.
SmellNoneSometimes water containing organic matter has a characteristic smell of humus.
TemperatureUnder 25°CIt is advisable to collect water with a temperature between 5 and 15°C.
pH6.9It should preferably be between 6.5 and 7.5.
OxygenThe maximumThis is the case with springs and streams. Stagnant and still water is not suitable.
HardnessUnder 16.8°GHBeyond 11.2°GH, it must be mixed with fresh water (except in rare cases, for certain fish).
AmmoniaUnder 0.4 mg/literThis value is rarely attained in balanced water.
NitritesUnder 0.1 mg/literThis is the drinking water threshold.
NitratesUnder 50 mg/literThis is the threshold for drinking water, often exceeded in farming areas.

Water Usable in Aquariums



Rainwater is soft and acid, so is useful for diluting water that is too hard. It should be collected in plastic containers; if these are put under a gutter, take care not to collect the first water, as this will have cleaned the roof. In urban and industrial areas, rainwater is liable to contain pollutants, and it is therefore not advisable to use it.

 • Stagnant water (ponds) and still water (downriver) Such water can pose a microbiological risk, and it is not advisable to use it.

 • Demineralized and distilled water Their pH is neutral or very slightly acid, with little or no hardness. Their high price means that they are only used for mixing with hard water, or for filling a small rearing aquarium. Do not forget that softened water cannot be used.

 • Bottled water This is often referred to as mineral water - erroneously so, as some brands contain hardly any minerals and are quite soft. These are certainly not used to fill up huge tanks, bottle by bottle, as this would be too expensive and time-consuming, and therefore serve a similar function to that of distilled water.

Characteristics of some bottled waters

The Next Aquarium Article : Sea Water Characteristics and information

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