Acquisition and introduction of the first fish.
The most common mistake is when fish are bought on the day the aquarium is purchased and immediately placed into it; in most cases, this leads to their death. Do not rush, setting up an aquarium takes time.
Usually, on the 8th-10th day after filling, when the water has become clear, fish can be introduced into the aquarium. You should not introduce all planned fish at once. The fact is that the filter has not yet “matured” and is not fully capable of providing the required level of water filtration. It is best to introduce only a few of the hardiest fish until biological equilibrium is fully established. A small number of fish will contribute to the faster “maturing” of the filter.
The bag with the purchased fish is untied, and the edge of the bag is secured with a clothespin to the edge of the aquarium. It is necessary for the temperature in the bag and the aquarium to equalize. This usually happens in 20-30 minutes. If necessary, provide the fish with mild aeration. It is also helpful to add an anti-stress preparation.
Secondly, it is necessary to equalize the chemical parameters of the water. To do this, you can periodically add water in small portions to the bag. The duration of this procedure depends on the difference in water parameters. (In practice, this entire procedure takes 30-60 minutes). Then you can net the fish and transfer them to a quarantine or holding tank. Do not pour the water from the bag into the tank, as there is a risk of carrying in infections and other troubles. Under no circumstances feed the fish during the first 24 hours. On the second day, food should be given in very small doses. Bring the amount of food to normal gradually.
For the first two months, you should feed the fish daily, observe their behavior, and occasionally remove rotting old plant leaves. When starting the aquarium, it is advisable to feed the fish with live or frozen foods; if dry food is used, feed them very little for at least three weeks with fasting days. Dry foods tend to decompose quickly, which can cause a bacterial bloom or poisoning.
Even when the aquarium and its filtration system have “matured,” the bacterial population will still be limited. It will not yet be able to cope with the load given by an aquarium full of fish eating a normal diet. Therefore, the load should be increased gradually. To begin with, acquire hardy fish (the quantity depends on the volume of the aquarium). Guppies, Danio, swordtails, marble gouramies, macropods, catfish, Corydoras will do. The fish should not be too sluggish, should not have frayed fins, sunken bellies, ulcers, wounds, white spots (resembling ich), tumors, or cotton-like growths, heavy slime production, or flared gills. Particularly demanding fish should not be bought until the aquarium is fully established, i.e., during the first two months.
Which snails are best suited for the aquarium? Ampullaria snails place their egg clutches above the water, and consequently, their population will be very easy to control. However, if you introduce bladder snails, pond snails into the aquarium, you will never get rid of them. Besides snails, you can introduce Amano shrimp, which have become very popular, into a new aquarium. They will quickly deal with lower algae if they suddenly appear.
It is very important to monitor the appearance of algae in the aquarium. The development of brown or green algae indicates that the lighting regimen is incorrectly selected and needs adjustment (the appearance of green algae indicates excess lighting, brown — deficiency). The filter sponge must be rinsed weekly to remove mechanical suspension. Starting from the first month, you can regularly perform 20-25% water changes.
Of course, everyone wants to achieve their goal as quickly as possible. You feel that the plants are not growing fast enough, and the recently purchased fish are growing painfully slowly. You pull out mineral salts to fertilize the plants and generously enrich the substrate in the aquarium with them. You hope this will help the growth of plants and animals, but in reality, you disrupt the natural development processes, which are the only way to achieve an aquarium of flawless purity and beauty. Therefore: excess is always harmful! It is bad if you constantly tinker with your aquarium. You should care for it only to the extent that is absolutely necessary. The less time and effort you spend on it, the better.
Remember that any interference in the internal life of the aquarium can disrupt natural biological processes, disturb the fish, and hinder plant growth. The same applies to feeding. Overfeeding is the cause of most aquarium disturbances. Clouding and spoiling of water, algae development, digestive disorders in fish, and their diseases — all these can be the result of excessive, abundant feeding. In short, if something is wrong in your aquarium, the cause should generally be sought not in the animals and plants, but first of all in yourself.
The good well-being of the fish, active plant growth, and the absence of excessive algae proliferation indicate that biological equilibrium has been established. The water in a settled aquarium should be transparent, with a slightly yellowish tint, and have the smell of freshly cut grass. Usually, a stable state in the aquarium forms 3-6 months after filling with water. Starting an aquarium is a long process.
Choice of fish for your aquarium.
Aquarium substrate. Aquarium plants. 
