What oak extract is supposed to do
Oak extract is used to lower the pH in the aquarium. The acids contained destroy the carbonate hardness. If the carbonate hardness is lowered while the water values are otherwise the same, the pH value also falls.
What oak extract is made of
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Different manufacturers offer products that are said to contain oak extract under different names. Since the ingredients are usually not listed, as is unfortunately common in aquaristics, it is not possible to check how much real oak bark extract is contained.
Statements such as “made from real oak bark” or “contains 100% oak bark” are not very meaningful.
«Oak bark» can also mean «oak bark and other acids».
Wordings such as “exclusively made from pure oak bark” or “100% made from pure oak bark” would be more meaningful. However, it is also difficult to produce a liquid product from 100% pure oak bark. Such a remedy would probably be a powder made from ground oak bark.
The main components of pH-lowering agents are usually hydrochloric, sulfuric or phosphoric acid. Instead of expensive means from the pet shop, the corresponding acids can be used more cheaply.
phosphoric acid
Phosphoric acid contains phosphates, which are absorbed by algae as nutrients. The advantage of lowering the pH is offset by the disadvantage that additional nutrients for algae are brought into the aquarium. A phosphate test can be used to determine whether the oak extract consists of phosphoric acid or another acid.
citric acid
Citric acid is not suitable for lowering the pH value. It is not a mineral acid but an organic acid that pollutes the water organically. Since citric acid is only slightly acidic, a relatively large amount of acid is required.
Because the organic compounds in the citric acid are broken down by bacteria into carbon dioxide and water, oxygen is used up in the aquarium. In extreme cases, this can lead to a severe lack of oxygen and a bacterial bloom. Due to the oxygen consumption, the carbonate hardness also increases again.
Other organic acids can also quickly lead to bacterial blooms. Tests have also shown that the pH value only falls for a short time and then rises again.
sulfuric acid
4% sulfuric acid is suitable for lowering the pH value. It does not pollute the water through bacterial decomposition and does not lead to eutrophication of the water. So, sulfuric acid does not cause bacterial blooms. The ion ratios in the water are not changed.
hydrochloric acid
3.6% hydrochloric acid is suitable for lowering the pH value. However, hydrochloric acid has no buffering effect. The buffer capacity of the existing carbonate hardness carbon dioxide buffer is reduced due to the reduction in KH caused by hydrochloric acid. This shifts the concentration ratio of carbonate hardness to carbon dioxide.
This concentration ratio in turn determines the pH value. Halving the carbonate hardness lowers the pH by 0.3 units. Because the carbon dioxide content is mainly determined by the biological components and the gas exchange with the air, the carbon dioxide content levels off at the old value again and again.
Hydrochloric acid and sulfuric acid change the ratio of the ions in the water to one another.
When using strong acids, such as sulfuric acid and hydrochloric acid, the hydrogen carbonate HCO3 contained in the water is expelled from the water and replaced by the respective acid. This changes the ratio of the ions to one another, the so-called ion spectrum.
Important NOTE
All acids, oak extracts, etc. may only be used outside the aquarium to treat the water. The pH value must be monitored. You cannot simply proceed according to the dosing instructions. Otherwise there is a risk that the water will be too acidic. Especially in soft water, a few too many drops are enough to cause a dangerous drop in acidity.
If the carbonate hardness is completely destroyed, the pH will drop extremely quickly, even if only a little acid is added to the water. At the same time, the conductance increases rapidly.
By destroying the carbonate hardness, carbon dioxide is released. This can produce dangerously high amounts of carbon dioxide for the fish. Filter bacteria can be damaged. If you try to expel the carbon dioxide by surface currents or oxygen stones, the pH rises again.
If the treated water is mixed with the old water in the aquarium, care must also be taken to ensure that the pH value of the mixed water does not suddenly drop. If water with a very low pH value is mixed with water with a very high conductivity, the same dangerous effects occur as when the acid is used directly in the aquarium.
Homemade oak extract 1
Dried and ground oak bark is doused with hot water. The thick bark on the trunk is not used for this. The oak bark referred to here is the thin bark on annual or biennial branches. The mixture must steep for 10 to 15 minutes. Then the liquid is filtered through a coffee filter, glass wool or similar. Since the concentration of the acid always fluctuates during your own production, the pH value and the carbonate hardness have to be measured again and again.
Homemade oak extract 2
The bark of the English oak (Quercus robur) is used to produce oak extract. The bark contains the following active ingredients: tannins, gallic acid, bitter substances and small amounts of pectins and resins. The bark has an astringent, ie astringent, effect on tissue, reduces secretions from glands and mucous membranes, has an anti-inflammatory and slightly antiseptic effect.
500 g of oak bark and 3 liters of water are boiled down to 1/3 of their volume. The still hot mixture is filled into sterile bottles, sealed tightly and stored in the refrigerator. Since very little of this extract is needed, small bottles will suffice.
The extract is strongly acidic. Therefore, the change in pH is used to adjust the dose. A cuvette is filled with aquarium water up to the 5 ml mark. The prescribed amount of pH test reagent is added and the pH is read. In a second cuvette, 1 ml extract and 10 ml distilled water are mixed. A pipette is used to add drops of this diluted extract to the aquarium water in the first cuvette until the pH value is 0.5 lower. The number of drops required is counted.
10% of the counted drops must then be added to 1 liter of aquarium water in order to reduce the pH value by 0.05. Higher dosages are possible, but should be avoided because of the side effects, e.g. B. due to the astringent effect on the gills, added very carefully.
alternatives
If the pH value is only to be lowered by a small amount and if the carbonate hardness is not too high, peat or alder cones can be used. The humic acids released in the process also have an anti-algae and antibacterial effect. If the carbonate hardness is high, however, a lot of peat is consumed. Excessive amounts of peat can pollute the water organically. In such cases, the water should first be softened, e.g. B. with an osmosis system, and then filtered through peat.
In principle, of course, the oak extract also destroys and reduces the carbonate hardness and then peat can be used.