the newly bought fish cannot be put in the tank with the old fish immediately, because it may carry disease, and even if it looks healthy, it may come down with morbidity later. Therefore, it is necessary to isolate them for a period of time, observe the physical condition of the fish, usually about a week, during which the fish should be disinfected.
There are many ways to disinfect, you can use potassium permanganate solution or salt water immersion, after a period of time out, so it can kill the harmful bacteria on its body, to prevent its damage to other fish. It should be noted that disinfection may cause it to roll over, and it needs to be given proper oxygen explosion in order to return to normal.
The first step in closing the tank is to overtemperature. Make sure that the water temperature of the container in which the new fish is placed is the same as that of the fish tank. You can put the fish in the bag first and soak it in the water ready for the tank, so that the temperature of the water inside and outside the bag will gradually be the same, so that the fish in the bag will adapt to the temperature of the tank.
After the temperature is too high, water should be passed, because the fluctuation of water quality may cause the stress reaction of fish, so it is necessary to test the water slowly. Scoop the water in the fish tank into the bag, then scoop the water out of the bag, wait for a period of time to find no problem, repeat this, after a few times the fish will be able to adapt to the new tank of water.
