15-11-2021, 22:15


The natural acidification of aquarium water with dried leaf litter is useful for the proper keeping of fish inhabiting Amazonian blackwater habitats as well as for shrimps, catfish and snails, for which these materials are natural food. There are some simple tricks and methods for using leaf litter and other organic material for naturally acidifying aquarium water.

First, you should be cautioned not to overestimate the possibilities of these natural methods for lowering the pH value in your aquarium. Tree leaves or peat will lower the pH value slightly and gradually, not abruptly and quickly. The difference between mineral acids and natural humic substances is that the former are much stronger, thus making it possible to acidify even hard tap water, which you cannot do with dry leaves or peat.

Also remember that these natural acidification methods are most effective when we are dealing with soft water. Natural pH reduction methods are certainly useful when keeping demanding fish or ensuring the health of rare and valuable specimens such as wild-caught fish, for which the use of more aggressive chemicals might be too risky. These methods may also be useful when preparing water for hard-to-reproduce species originating from blackwater habitats - after they have been placed in an aquarium.

By using peat, leaves or other natural methods, we gradually lower the pH value while tinting the water coloured with cola and introducing valuable organic compounds (tannins) which, among others, disinfect the water. Dried tree leaves also make an interesting natural decoration and serve as a refuge for smaller fish. Some species lay their eggs among them and newly hatched fry find numerous micro-organisms on their surface, which they may feed on during their early days. During leaf decomposition, the water parameters in the aquarium approximate those of a stream or river flowing through a woodland.

There is no clear answer to the question of how many leaves you should put in the aquarium for the desired effect. It depends on many factors, including which tree the leaves come from, their size and the existing parameters of your water. Everyone should experiment by trial and error to find the "golden mean" for their individual settings.

Dried tree leaves

Oak is widely distributed all over the world, and its characteristic leaves are sure to add charm to any aquarium. They should be dry (the concentration of tannins in dry leaves is several times higher than in green leaves), collected in places away from sources of pollution, such as roads or factories, and free from fungicides and pesticides, which can result from collecting leaves in the vicinity of arable fields.

It is best to take leaves that have fallen from the tree or to collect them after the first frost. In addition, they should be collected in autumn (not spring), ideally when the weather is dry and it has not yet rained, as rain can wash valuable compounds out of them. They should also be healthy and undamaged, without stains or colour changes. Dry leaves can immediately be put into the aquarium - but it is best to press them down with a heavy object, otherwise they will float. Alternatively, take a few litres of reverse osmosis water and place a handful of leaves in it for a few days, then measure the pH value. The water, together with the leaves (which should sink in on their own after soaking), can then be gradually poured into the aquarium. The pH value should be monitored until it stabilizes and the desired effect is achieved.

Other useful and just as effective as oak leaves for acidifying the water are beech leaves, which slightly reduce the pH value in the aquarium, and hornbeam leaves, which quickly and significantly reduce the pH value.

We also use leaves from trees such as common maple, poplar, birch, hazel, sycamore and maple in the aquarium hobby.

Walnut leaves are another option. As well as acidifying water, they have anti-inflammatory, bactericidal and fungicidal properties. These leaves should be harvested green and then dried. Walnut leaves are a valuable addition to the diet of dwarf shrimp. If the leaves are steamed first, they will release tannins faster, and your shrimp will feed on them faster.

White mulberry leaves are also used. They contain tannins and organic acids, are a source of protein and amino acids, and also contain vitamins and minerals. Like beech leaves, they should be harvested while still green and then dried.

For leaves that can be purchased from aquarium shops, consider Terminalia catappa, also known as Indian almond or ketapang. Liquid extracts and bark of this tree are also available. This tree grows mainly in the tropical regions of Asia, Africa and Australia. The dried leaves of the Indian almond tree are used in shrimp farming because they naturally improve the water quality in the aquarium. Cetapang releases natural tannins into the water and lowers the pH, creating an environment similar to a blackwater biotope.

Indian almond leaves also reduce the harmful effects of heavy metals in the water. When exposed to water, the leaves release humic acids and tannins. Ketapang leaves have been known and have long been used in Asia by owners of blackwater fish and shrimp. They are one of the best natural remedies for improving conditions in aquariums, whether ornamental or intended for breeding. Known for their antibacterial and antifungal properties, they improve the condition of fish suffering from fin rot, wounds and abrasions.

The leaves of the Indian almond tree are also useful for the daily prevention of disease in fish and shrimp, improving fecundity and enhancing colouration. In Asia, cockerel breeders use the dried leaves as bubble surfaces and to introduce substances that protect the fry from disease. As a bonus, the decomposing leaves in the aquarium turn into detritus on which colonies of micro-organisms grow that the fry can feed on.

Ketapang leaves not only acidify the water, but also:

  • accelerate the regeneration of mucous membranes, epidermis and fin tissues;
  • reduce the risk of fungal diseases in adult fish;
  • protect the eggs from fungus;
  • increase the survival rate of fry.

They are also a food source for shrimps and catfish - after a few days, when the leaves are well wet, the shrimps start to eat them until only a few veins remain.

Alder cones

Cones of black alder (Alnus glutinosa), a tree from Europe that grows near marshes and ponds, are used in aquariums to lower the pH value. These cones are also used in spawning tanks, where they stimulate the spawning of some species and prevent fungal growth on the eggs.


Peat is usually available in various forms in aquarium shops:

  • liquid (peat extract);
  • fibrous (its natural state);
  • Pelleted (processed or pressed, which makes it stronger and more durable than the fibrous form).

The last two types of peat are also used as filter media, often in canister filters.

As with leaves, the peat method is largely based on trial and error. It is up to you to determine how much peat you need in your own aquarium to reduce the pH value of the aquarium water to the desired value, because not all peat is the same, and its humic acid content may vary widely. The dosing should follow the manufacturer's instructions.

Humic substances contained in peat are most effective in soft water. It is advisable to check the alkalinity or carbonate hardness of the water beforehand, because in the presence of high alkalinity the effect of any pH lowering material will be very short-lived. This is why it is advisable to soften harder water in advance, for example by adding reverse osmosis water.

When talking about peat, mention should also be made of lignite, which is an intermediate phase between peat and lignite (developmental stage of lignite). It is used for aquarium decoration, often as a background or for shelter plants, often with planted mosses or anubias. Depending on the quantity, quality and origin, lignite may slightly acidify the water due to its humic compounds. It also enriches the water with minerals and may serve as a spawning substrate for fish such as aguaruna, discus or catfish. As with peat, you need to experiment to determine how much lignite to add to lower the pH.

Beware of an overdose of tannin

Organic tannins are natural substances found in plants, including their leaves. They have a bacteriostatic effect and act as an antiseptic, protecting the plant from fungi and insects. Their bactericidal action consists in binding to proteins to form insoluble compounds. In this way the development of the bacteria consisting of proteins is stopped and therefore the tannins have a certain medicinal value.

Tannins are water-soluble, and they are used in aquariums to limit bacterial growth. If used in moderation, they may also be involved in other processes, such as protecting the eggs from fungal diseases that cause their death.

Unfortunately, it is possible to unintentionally overdo the tannins in the aquarium by using too many leaves or too much peat. Too high a concentration of tannins in the water causes coagulation of the fish mucus, which may, among others, lead to sticking of the gill filaments, disturbing the gas exchange and potentially causing suffocation. Suffering fish can be observed suffocating near the water surface.

Skin irritation due to excess tannins can also occur. When something like this happens, the only remedy is an immediate large water change and, if there are leaves or peat fibers in the tank, these should be removed immediately. Remember that leaves, peat and their extracts should be dosed moderately and carefully.

Natural additives

Adding materials such as dried tree leaves and peat is becoming an increasingly popular way to lower the pH value in the aquarium. Leaves can also be used in many different ways - as decoration, as food, for creating the right atmosphere in the aquarium and for adding a natural look to the bottom, similar to the leaf litter substrate typical for rivers and streams in the Amazon and southeast Asia.

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