Introducing newly purchased fish and plants into the aquarium.
Upon coming home, there is one last but very important thing left to do – to correctly introduce them into the aquarium. As it turns out, there is a science and a strict order of operations to this, ensuring a gentle transition of the fish into their new living conditions. A novice aquarist might be surprised by how many complications are hidden within this seemingly obvious and simple action, and without much thought, might just take and pour the newly brought home fish directly into the aquarium along with the water they “travelled” in.
Do not be surprised later if both these new fish and the old-timers soon begin to die. In reality, newly acquired fish should first undergo quarantine in a specially equipped quarantine tank and only then can they be placed in the main aquarium. Some plants react to a sharp change in water composition by dropping their leaves. For a beginning aquarist, the adaptation process must be performed for any new fish, without exception.
The modern development of aquarium keeping worldwide is currently impossible without a regular supply of wild inhabitants from natural tropical water bodies to hobbyists. Fish bred for aquarium keeping in aquaculture systems, mainly of Asian origin, are usually raised in ponds and open concrete pools where they may be exposed to specific diseases, sometimes quite serious, which do not show symptoms. However, this inevitably leads to infection and epizootics in the enclosed conditions of home aquariums, as well as due to stresses associated with catching, transportation, changes in maintenance conditions, feeds, etc.
To reduce the risk of infection, you should first of all purchase Cichlidae from importers with a good reputation. This may prove to be a more expensive pleasure than buying from unknown sellers, but it guarantees safety from the unpleasant consequences of infection and the death of all aquarium inhabitants. Therefore, for full assurance, you should also, if possible, quarantine newly received fish, especially from an unknown or dubious source.
You can introduce fish directly into the general aquarium only if they are taken from a known and reliable aquarium source; otherwise, to prevent introducing diseases, new fish should undergo a monthly quarantine (and fish obtained from natural water bodies or brought from abroad, a 2-3 month quarantine). When introducing one species of fish to another, you should take into account their temperament, behavior, and compatibility. Fish that prefer different dwelling levels, are not food competitors, and have dissimilar coloration get along most successfully.
Do not overpopulate the aquarium. Overpopulation in an aquarium is one of the main sources of trouble! In an aquarium with a filtration system, aeration, and live plants, for small fish (Tanichthys albonubes, neon tetras, zebrafish, rasboras) 1.5 liters per fish is required; for medium fish (tiger barbs, guppies, platies, swordtails, small catfish, labyrinth fish) – 4 liters; for large fish (small and medium Cichlidae, medium catfish, large Cyprinidae) – 15 liters per fish. These figures are very approximate; it is advisable to find out the optimal volume for keeping each fish in the aquarium. The sum of such optimal volumes for each fish must not exceed the volume of water in the aquarium.
Fish are animals with a variable body temperature. Their temperature depends on the water temperature and in most fish exceeds it by only 0.5-1 degree. For each fish species, there is an upper and lower temperature limit. If this limit is violated, the fish dies or at least gets sick. If they are transplanted from warm to cold water, they enter a state of shock. They swim slowly or lie motionlessly at the bottom and eventually die. The movements of the gill covers slow down or stop altogether. Very often, the shock state ends in the death of the fish. When transplanted from cold to warm water, they dart around the aquarium, trying to jump out of the water. If the water in the bag is too cold, the fish’s swim bladders will immediately become inflamed, which is easily recognized by an atypical swimming pattern.
To avoid this, fish should only be transplanted when the temperature in the bag they were brought in from the store equalizes with the water temperature in the aquarium. A difference of no more than 2 degrees from warm to cold and 4 degrees from cold to warm is permissible 
. The water temperature in the aquarium should, if necessary, be lowered or raised gradually. Sometimes it is necessary to carefully monitor not only the water temperature but also the air temperature above the water. This is especially important when keeping labyrinth fish that regularly gulp air from the surface. Quite heat-loving Siamese fighting fish (bettas), gouramis, and dwarf gouramis can get sick or even die by “inhaling” air that is 5 degrees or more colder than the water where these fish live.
Characteristic signs of a cold-related illness when keeping fish at low temperatures are as follows: general weakness manifested by low mobility of the fish; clamped fins; fading of body color; refusal of food. Fish stay near the reflector or in the upper layers of water near the heater. Remaining in one place or slowly moving forward, they make oscillating movements with their whole body. Often, individual areas or the entire body become covered with a grayish-white coating. With a significant increase in water temperature, fish stay in the upper layers, greedily gulping atmospheric air. This is explained by a decrease in the dissolved oxygen content in the water necessary for respiration. Fish suffering from a lack of oxygen should be transplanted into clean, oxygen-rich water as quickly as possible.
It is best to transplant newly acquired fish with the lighting turned off for 2-3 hours. In the dark, fish adapt more calmly to new conditions and new neighbors. During the first day, it is better not to feed the aquarium inhabitants; give them time to acclimatize.
Some fish species require long-settled (“old”) water, while others, conversely, prefer fresh water. However, in all cases, it must be remembered that fish should not be introduced into tap water that has stood for less than a day, since tap water is disinfected by chlorination, and chlorine is detrimental to fish. In addition, too much oxygen can be dissolved in fresh water, which is also harmful to fish.
Touching upon the topic of wild fish adaptation to captivity, one of the most important conditions under which adaptation will proceed most smoothly should be noted: freshly imported fish should be placed in an aquarium with an established biological balance (the so-called “old” aquarium). Any aquarium where fish have already lived for at least 2 months satisfies this condition. Under no circumstances should newly purchased fish be placed in fresh tap water, even if it has been settled for a long time. “Old” water contains all the necessary substances and bacteria required for the rapid adaptation of fish.
However, the term “old” water should not be understood in the sense often implied by breeders of characin fish – for “characin breeders” this term can even mean “water not changed for months.” By “old” water for African cichlids, we mean water in which fish have lived for a long time in good or excellent health (including weekly water changes), and by an “old” aquarium – a tank where fish have lived for at least 2 months.
In an “old” aquarium, the adaptation of new fish is maximally guaranteed, provided that its previous inhabitants were in full health and excellent well-being. If you want to acquire wild fish and place them in a new aquarium, it is recommended to perform an initial 2-month “settling in” period with other fish. In extreme cases, you can do the same as when starting a new aquarium – place a certain amount of substrate from the “old” aquarium (300-500 grams) into it, fill it a quarter to a third with “old” water, and install a filter sponge from an operating “old” aquarium.
In this way, with a minimal risk factor, you can quickly start a new aquarium to introduce new residents, including wild ones. Fish and demanding plants are introduced into a new aquarium when the water clears and previously planted plants produce fresh leaves. This occurs in 9-14 days, and full balance and equilibrium are established in 3-4 months.
Transferring African cichlids from aquarium to aquarium upon reaching sexual maturity is tolerated very easily – they cope well with adaptation to a new landscape and a larger volume. Transferring to a smaller volume, especially adult fish, may not always end successfully, however. This is associated with the sad reputation of cichlids as great brawlers and killers. In reality, the following situation is often observed: a novice aquarist acquires adult fish and releases them into their aquarium without inquiring about the water volume in which the purchased fish lived with their previous owner. If the aquarium volume is significantly reduced compared to their previous home, a tragic end for the weaker ones is guaranteed. Alas, cichlids do not like such experiments. After forming a school, the aquarium should be additionally equipped with spawning substrates characteristic of the given species and hiding places.
When a new fish is introduced into an aquarium where “territorial” species already exist, it usually becomes the target of attacks. This typically baffles the aquarist, especially if the new fish was acquired as a spawning partner for an already existing fish of the same species, and therefore they expected the new fish to be a welcome neighbor. However, the territorial fish sees the newcomer as an uninvited guest, unless the new fish is ready to spawn immediately.
In some fish groups, territory establishment and pair formation for spawning are interrelated processes, with pair formation often preceding “territory marking.” Otherwise, it is necessary for the partner without a territory yet to approach the partner who already has a plot, giving the correct courtship signals. But this does not happen when a new fish, confused by an unfamiliar environment and stressed from transportation, is unceremoniously dropped into a territory already belonging to another fish.
However, remember that even very competently performed fish transportation, and even simply transferring it from one aquarium to another, inevitably involves stress for the fish, which must be mitigated. This is most important during the first day of the fish’s stay in the new place, when its immunity is especially vulnerable. During this period, it is imperative to add anti-stress and mild antibacterial agents to the water. If you are absolutely sure that the imported fish is healthy, then some brand-name product is quite sufficient for this: Aqutan (Sera), AquaSafe (Tetra), StressCoat (Aquarium Pharmaceuticals), or an equivalent from another manufacturer. These products reduce stress, promote rapid healing of damaged skin and mucous membranes, and facilitate fish adaptation. It won’t hurt, just in case, to add a small amount of methylene blue or malachite green-based products to the aquarium.
These medications, especially in preventive doses, do not harm plants. There is no need to change the water after using them: in a couple of days, the medications decompose on their own in the aquarium water under the influence of light, filtration, and aeration. And watch the fish very carefully in the first days after relocation so as not to miss possible early signs of any diseases and to start appropriate treatment immediately. Ozonized water is also used to disinfect newly acquired fish and plants. To disinfect newly acquired plants, it is sufficient to immerse them for 20-30 minutes in freshly ozonized water.
As a rule, neither filters, nor aeration, nor UV sterilization need to be turned off while using adaptation medications. But there are exceptions. For example, if you are using antibiotics, the UV sterilizer must be turned off, because under the influence of ultraviolet light, all antibiotics (except furan derivatives) decompose, forming compounds toxic to fish. And finally: while using any medications, remove activated carbon from the filter (if you use it), otherwise it will very quickly absorb the medications you introduced and nullify your efforts.
Transferring fish to different water, or what to do with newly acquired fish?
How to choose and buy aquarium fish? Where are fish purchased? 
