What are the ways to cultivate good water for fish keeping?

As the saying goes, to keep fish you must first cultivate the water. So, how do you cultivate good water?

Everyone knows that tap water straight from the faucet is not suitable for keeping fish directly; you must first remove chlorine and increase oxygen, and for higher requirements, you also need to adjust the water's hardness and pH. We usually call the treatment of water before it goes into the tank “making water”; of course, making water can also be regarded as one stage of cultivating water.

Is water that has been dechlorinated, oxygenated, and had its hardness and pH adjusted considered good water? Judging by the commonly used test indicators, it can be considered good water, but this kind of water has two drawbacks: first, it is not stable enough; second, it is relatively “lean.” Keeping fish with properly made water will soon cause the water quality to change, because it lacks self-purification capacity; properly made water is usually quite clean, with almost no harmful substances, but at the same time it also lacks things beneficial to fish and other organisms.

Storing fresh tap water in an open water storage container for a period of time is very helpful for dechlorination and oxygenation, but this is still not what we mean by cultivating water. True water cultivation must take place in an aquarium, and can only be carried out under conditions where fish are present.

1. Setting up a new tank is an important stage of cultivating water; whether the foundation is laid well has a great impact on the future.

After tap water is put into a new aquarium and subjected to aeration for dechlorination and oxygenation, pioneer fish can be introduced. Once there are fish, there is a source of organic matter in the water, whose main components include carbohydrates, fats, proteins, and so on. The accumulation of these substances pollutes the water, and at the same time, microorganisms that live on organic matter, mainly various heterotrophic bacteria, begin to multiply in large numbers. The products of organic matter decomposition in turn attract new microorganisms. Among them, ammonia produced by the decomposition of nitrogen-containing compounds such as proteins provides food for nitrifying bacteria, so nitrifying bacteria begin to multiply. In addition, various plankton, protozoa, and others also appear one after another. The organisms and various components in the water tend toward diversification and form a simple food chain, and the water begins to have activity.

Nitrifying bacteria include two categories: ammonium-oxidizing bacteria (also called nitrosifying bacteria) and nitrite-oxidizing bacteria (also called nitrifying bacteria). They can effectively decompose ammonia, which is toxic to fish, and the nitrite it is converted into, so they are of particularly great significance. The main sign of whether tank setup is successful is the establishment of the nitrification system; the ability to remove ammonia and nitrite is also an important indicator for measuring the water's self-purification capacity.

Various types of bacteria do not only live in the water. On the tank walls, bottom sand, and other solid surfaces inside the tank, large amounts of bacteria grow attached. Nitrifying bacteria mainly live attached to object surfaces; in the water itself, their numbers are instead very low, and they lack activity. Many heterotrophic bacteria are also more active when living on fixed surfaces. In fact, cultivating water mainly means cultivating microorganisms, that is, establishing a good microecological water environment, which includes the various elements of the water body, the tank body, and the filtration system. Away from the tank, the stability of the water will decrease. By the same reasoning, a mature, good tank will not have the stability of its water destroyed by routine water changes.

During the tank setup stage, adopt some strengthening measures and equip a powerful filtration system, including sufficient filter media.

We generally divide filter media into three major categories: physical filter media, chemical filter media, and biological filter media. In fact, most physical and chemical filter media also simultaneously have a biological cultivation function. The purpose of configuring biological filter media is to provide sufficient attachment surfaces for various types of bacteria. In an aquarium, if the growth and reproduction of bacteria are limited by living space, it is difficult for them to adapt to the load of high-density keeping. Using filter media to expand the living space of bacteria can achieve a stronger self-purification capacity than under natural conditions.

According to the attachment and growth characteristics of nitrifying bacteria, providing them with appropriate living space is the basic condition for establishing a powerful nitrification system. There are many types of filter media suitable for nitrifying bacteria to attach to. We usually choose materials with a large specific surface area to reduce the volume of the filter. On the premise of satisfying the growth and reproduction of nitrifying bacteria, we should also consider providing suitable conditions for culturing heterotrophic bacteria.

Heterotrophic bacteria use various enzymes they secrete themselves to decompose organic matter. Some bacteria can produce extracellular enzymes; these enzymes are released into the water, and the bacterial cells can decompose and absorb without needing to attach to the organic matter. But some bacteria can only produce surface enzymes, meaning the bacterial cells must attach to the organic matter in order to decompose and absorb it. There is more organic matter on filter cotton, and this is also a place where heterotrophic bacteria multiply in large numbers. Whether filter cotton should be washed and replaced frequently cannot be generalized. Generally speaking, as long as the filter cotton is not clogged, it does not need to be cleaned (or replaced). Besides filter cotton, bio-cotton can also be used as a bacterial bed, because its pores are relatively large and it is not easily clogged, which can greatly reduce routine maintenance. Bottom sand is also a good filter medium; it can cultivate both nitrifying bacteria and heterotrophic bacteria. In addition, bottom sand can form local anoxic zones, which is favorable for the growth of certain anaerobic bacteria.

2. Ensure adequate oxygen supply.

The decomposition of organic matter consumes large amounts of oxygen, which will cause the oxygen content of the water body to decrease. This not only threatens the survival of fish, but is also unfavorable to the growth and work of aerobic bacteria. Promptly replenishing the loss of oxygen in the water is of particularly great significance when the concentration of organic matter is high. Nitrifying bacteria are typical aerobic bacteria; when oxygen is lacking, they cannot effectively oxidize ammonia and nitrite, and when ammonia and nitrite reach a certain concentration, they can also cause fish death.

The efficiency of the filtration system is directly proportional to the oxygen content. Using trickle or breathing (tidal) filtration methods with good oxygen supply can accelerate the growth of the bacterial film. If other filtration methods are used, in addition to increasing the dissolved oxygen content of the water body, you can also consider carrying out local oxygenation of the filtration system.

3. Actively introduce beneficial bacteria; you can choose nitrifying bacteria or a composite bacteria product (containing nitrifying bacteria) and add it to the aquarium.

Nitrifying bacteria are everywhere; as long as suitable conditions exist, they will multiply. But nitrifying bacteria are autotrophic bacteria and must synthesize organic matter within their bodies, so they reproduce relatively slowly. If a sufficient amount of nitrifying bacteria is added to the aquarium, the establishment of the nitrification system can be accelerated.

In addition to nitrifying bacteria, composite bacteria products also contain some other beneficial bacteria, and their use is recommended. Beneficial bacteria can not only efficiently clean up organic matter in the water, which is conducive to forming a good microecological balance, but also produce some beneficial metabolites (mainly secondary metabolites), such as antibiotics, growth hormones, vitamins, alkaloids, and so on, which have positive effects on suppressing harmful bacteria and promoting plant growth.

Under normal circumstances, after about one month or so, the nitrification system can be initially established, and the concentration of organic matter in the water also drops to a relatively low level. At this time, fish can be formally kept.