Blackwater aquariums
What is black water?
So-called "black water" refers to aquarium water that manifests itself primarily in a brownish to berserk appearance. It is also very acidic and soft water, which has almost no measurable carbonate hardness and a very low conductivity of just 10-15 microsiemens in places, as well as a very low pH value. In nature, rotting plants, but also leaves in the water, as well as roots and branches of trees form acids that stabilize the pH value. This is usually very low and ranges in places between 3.5-5.5. The dark color is caused by dissolved tannins, humic acids, saponins and flavonoids from leaves, cones and roots. Depending on the amount of plant input, the water is therefore more or less dark. Compared to "normal aquariums", which on average tend to aim for acidity values around 6.5-7.6, it is easy to speak of "extreme" pH values in black water.
For whom is black water suitable?
Basically, when caring for ornamental fish in the aquarium, it is important to keep them as close to their natural habitat as possible in order to meet their needs. Fish from blackwater rivers, such as the Rio Negro, but also South American tetra species, are very well suited for keeping in a blackwater aquarium. Nevertheless, some also originate from Asia, which is why the pure designation as an Amazon tank can be misleading in places. Also other fish originate from soft water areas, but are not necessarily dependent on extremely low values and should rather not be kept in black water, if they do not originate from there. Likewise, pure blackwater fish should better not be kept in ordinary average water. Some soft water fish can be kept in aquariums with a slightly higher pH without any problems, but they need rather low extreme values for reproduction. In the wild, some fish also tend to migrate and seek other water parameters to breed, which they leave again after successful mating. Therefore, when breeding, these are initiated externally if they do not match the husbandry parameters. "True black water" can also counteract the development of algae in the aquarium, as the water has a more or less minor light-filtering effect and thus inhibits the growth of algae. However, this is not a problem for higher aquatic plants, especially those that originate from blackwater areas anyway or can cope with less light.
Photo: @aquarium.by.bddnk
Blackwater equals blackwater?
Nevertheless, one should distinguish between "real" and "imitated" black water, because not every aquarium that shows a yellow coloration also corresponds to the basic idea. With the help of so-called pH reducers or carbonate reducers, pH and KH are corrected downwards. Often various means are offered in the trade, which cause "only" a water coloration, but do not correspond to the associated biology. Sometimes it even happens that these products "work" on the basis of hydrochloric acid, which bring the water parameters down for a certain period of time, but ultimately have an influence on others and do not represent a permanently stable equilibrium, which in turn can affect the health of the animals. In principle, therefore, they should be used with caution, because often the concentration of the mixtures used are also risky and consist of inorganic sulfuric and phosphoric acids, which are difficult to dose correctly. It is therefore safer to handle the individual pure acids, which are also easier to handle and administer due to their known concentration.
Making black water yourself
Often the self-mixing of black water is the means of choice in the care of sensitive fish and no letter with seven seals, if you are somewhat familiar with the subject. Nevertheless, due to the low or even absent carbonate hardness, which acts as a pH buffer, a delicate touch is required to prevent acid falls. Therefore, the stability of the parameters should always be the main focus in order not to endanger the fish. Nevertheless, black water has a number of positive properties that make its use worthwhile. Above all, the run-in phase can be reduced considerably, and the need for medication is also reduced to a minimum. Last but not least, the reduced algae development with improved plant growth at the same time also speaks in favor of black water.
Photo: @aquarium.by.bddnk
Producing black water with the help of leaves and cones
As in nature, blackwater can be produced by maceration. To do this, leaves and alder con es are soaked in water, which dissolves out tannins, humic acids, saponins and flavonoids, among other things. Depending on the temperature, this can take between one and one and a half months, which is why changing water should always be done in good time. However, the types of foliage used should also be chosen carefully, as some can have toxic effects. Preference should be given to deciduous trees such as walnut, copper beech, chestnut or oak. The brown leaves should also be sourced away from roads or industrial areas. The dosage of alder cones should also be chosen carefully, because here too the dose makes the poison. Although alder cones very quickly release various substances, such as humic acid colorants and tannins, but in too high a quantity can have a deadly effect on the fish stock, as they have an antibacterial effect, among other things, so preference should always be given to foliage, the same applies, as already mentioned, stable water parameters. It is also important to use dry leaves and dry alder cones, because the residual moisture present in the leaves during the maceration process can otherwise lead to mold. Collected leaves or alder cones should therefore always be completely dry before use.
Using osmosis or rainwater (which has been collected openly and not run off and collected via gutters or roofs), the foliage is soaked and is ready for use after some time. If rainwater is used, filtering is recommended. In any case, the soaking process is preferable to boiling, since boiling can volatilize useful substances that are conducive to the acidification of water. It would also be possible to mix the boiled decoction of sea almond or walnut leaves, but their sole use is usually not sufficient to achieve the desired result. Measuring, monitoring and adjusting the water parameters should not be ignored.
Making your own black water with peat
When making black water, it is possible to introduce various pests such as planaria, dragonfly larvae or hydra, especially if the soaking barrels are left outside uncovered. Although these are considered snacks for various fish in places, they can become a hazard if invertebrates are maintained at the same time. This can be reduced by briefly scalding (not boiling!) the leaves beforehand. After soaking and leaching, this foliage can also serve as a food source for herbivorous species, such as catfish, if it is subsequently added to the aquarium. An alternative is therefore the use of peat.
In peat filtration, the unfertilized peat is added to the filter chamber or its boiled decoction is added to the aquarium water. However, the use of a peat cannon is just as good. Basically, with purchased peat it should be ensured that it does not contain any fertilizer, as this may catapult the phosphate and nitrate values upwards. Peat can also be added to the substrate, some fish like to bury themselves in it. If peat is used, osmosis water should always be preferred, as rainwater can often still have a carbonate hardness of 1-2 and the creation of "real black water" is therefore not feasible.
There is certainly no shortage of things to talk about when it comes to the controversial topic of "black water". Therefore it can be quite recommendable to let an experienced aquarium enthusiast of one's confidence take care of blackwater fish from South America, Asia or Central Africa. Ultimately, however, a beautifully maintained blackwater aquarium is a harmonious eye-catcher in the living room that can easily become a WOW factor.