Nadine
Age: 42
Joined: 23 Jan 2006
Posts: 26
Location: Germany
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An important topic in aquaristics is water hardness. It is quite a complex subject about which opinions are divided.
With this article we want to give you a general overview over this topic.
Water hardness and its meaning for aquaristics
Introduction
Water hardness is generally indicated as total hardness (°dGH).
Total hardness, however, is made up of two different parameters, whereby only one is of importance in the aquarium.
Total hardness can be split up into carbonate hardness (KH) and non-carbonate hardness (NKH).
For aquaristics, primarily the carbonate hardness is important, because this affects the carbon dioxide content (CO Č) and the pH value.
The carbonate hardness has been indicated so far in German degrees of hardness (°dKH). Often it is also indicated as temporary hardness, since it is driven out when water is boiling.
The non-carbonate hardness is e.g. the amount of other salts, like sulfates. The quantity of non-carbonate hardness is usually smaller than that of carbonate hardness. For aquaristics, non-carbonate hardness is relatively insignificant, however the total hardness should of course meet the requirements of the tank inhabitants.
The sum of carbonate hardness and non-carbonate hardness forms the total hardness.
The non-carbonate hardness is also called permanent hardness, since it is not driven out when boiling.
You can find an overview of the degrees of hardness here in the forum:
http://crustaforum.com/topic,29,-water-hardness-degrees.html
The carbonate hardness is an acid buffer, which means that it helps avoid or at least keep in check fluctuations in the water's acidity.
For this reason, carbonate hardness should never go below 3-4 °dKH, since otherwise the pH can drop or rise sharply in a very short time (also see the article re pH in the knowledge base).
Carbon dioxide (COČ) is usually stored by the carbonates and thus the pH is stabilized. If there are not enough carbonates (°dKH < 3) in the water, COČ can no longer be sufficiently buffered.
If a lack of CO Č occurs, the pH value can rise very quickly into the alkaline range (even over pH 9). A lack of COČ can easily arise in densely planted tanks without addition of COČ from the outside.
When there is a surplus of COČ the pH can drop just as quickly into acidic ranges (under pH 5).
As the content of COČ is subject to constant fluctuations, so is the pH. Most organisms in the tank do not tolerate this easily. When the pH moves into extreme value ranges, the inhabitants' deaths can probably not be avoided.
Many tank owners measure the water's electrical conductance in order to determine the degree of hardness (soft or hard). The higher the conductance, the higher the total hardness of the water.
Principally, water hardness plays a crucial role in the water's electrical conductivity. Unfortunately, however, the conductivity does not give any information about the size of the carbonate hardness share in total hardness; therefore the determination of the conductance is only of limited use for measuring water hardness in aquaristics.
There are several methods to determine water hardness; for the reasons stated above I won't go into detail about conductance measurement.
One method of determination is the use of test strips. Hold one of these strips into the tank water for just a second and wait for a short time. The strip will change colors and you can determine the hardness on the basis of a given color table.
Unfortunately these test strips are by no means exact and for this reason cannot be recommended without reservation.
When handled correctly, liquid measuring chemicals are more exact. You take a certain quantity of tank water (given in the instructions) and add drop by drop of the testing solution.
Depending upon hardness the water changes colour and on the basis of the number of drops water hardness is determined.
Both methods can be applied to determine total and carbonate hardness. You get the non-carbonate hardness by simply subtracting the carbonate hardness parameter from total hardness.
Sometimes it may occur that the parameter for carbonate hardness is actually higher than that for total hardness. Since this is, in fact, impossible, one ought to be inclined to think that this is a testing error. Of course, errors can occur, but usually there are other reasons for this. When testing GH we measure the water's total hardness defined as sum of all alkaline-earth ions dissolved in the water. Most KH tests measure, however, the acid capacity in mmol/l down to pH 4.3. Multiply this by 2.78 and you get the KH. This, however, does not correspond exactly to the defined carbonate hardness, in which only the alkaline-earth ions count. When measuring the acid capacity, however, all carbonates and hydrogen carbonates are considered.
In over 90% of the measurements this is unimportant, since the non-alkaline-earth ion concentration in water is usually very low.
Thus we measure two distinct parameters and yet assume they are the same. Strictly speaking, we would have to measure total hardness and the acid capacity and not connect these parameters in any way.
However, there is no practical sense in considering GH and KH separately since they do not deviate substantially from the definition in 99% of all cases. Moreover, when you change one of these parameters, both of them are usually affected.
Influencing water hardness
Since water hardness should be fit the requirements of the animals you keep it might be necessary to adapt it.
The usual case is that the water is too hard for the animals you'd like to keep.
Therefore we'll deal with lowering water hardness first.
One can lower the water hardness with various methods:
- Fully desalted water: If you mix your tap water with fully desalted water, e.g. distilled water or water from a reverse osmosis plant, both carbonate hardness and non-carbonate hardness will decrease in the same proportion.
- Peat filtering: By using a peat filter you will get down carbonate hardness easily and efficiently, since the pH is lowered by this method. This does not affect non-carbonate hardness.
- Cation exchangers: Here the carbonates are extracted from the water and thus carbonate hardness is lowered. Non-carbonate hardness is not affected here. There are, however, also ion exchangers that desalt the water entirely.
You should be very careful when softening your water; as I have written above, if carbonate hardness is too low, as a consequence the pH can become unstable.
In order to increase water hardness you can put calciferous rock into the water; another means is filtering over coral stone rubble for a longer period of time. If the desired water hardness is reached you should remove the coral stones.
If the water has gotten too soft (or too hard) you can of course readjust the parameters by mixing with hard (or respectively soft) water.
Many aquaristic dealers offer chemicals that can be added to the water in order to change the hardness, however, I do not advise newcomers to use these.
These chemicals are effective, but the danger of unsettling the sensitive biologial equilibrium of a tank for quite a long time is too high for me.
In my opinion, this is better suited for experienced tank owners who know what they're doing and have sufficient knowledge of water chemistry.
Conclusion
I would like to express my sincere thanks to other tank owners who have explained this subject to me.
I would like to especially mention Jani from the Zierfischverzeichnis forum
(www.zfv-forum.de), he gave me some input and references when I had fallen prey to some misunderstandings.
German version written by Christian (chrisp)
http://www.garnelenforum.de/board/cmps_index.php?pageid=Artikel |
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