Re-Create A Natural Environment
Fish adapt easier and faster if their habitat resembles its natural habitat; making them live happier. Live plants, right temperature and lighting are the most common factors to consider. If your fish naturally lives in vegetated waters, make sure to put plenty of live plants and even corals that can provide hiding spots and places to swim around. Live plants also provide oxygen and filters out harmful elements such as ammonia, nitrite, phosphate, and nitrate.
Some fish also prefer to live in lighter conditions, and some in darker. In the case of the former, make sure to put enough aquarium lights. Get a good aquarium heater if your fish prefer higher water temperature. Watch out for any drastic changes in your aquarium water temperature.
Choose The Right Tank Size
When there is not enough space in the aquarium, some fish feel terrirorially-challenged and turn aggressive against other fish. So depending on the volume of fish you wish to keep in your tank, choose the right tank size where they can swim freely as they grow.
Choose The Right Tank Mates
Not all fish are compatible with other fish varieties. Make sure to do your research which fish can live harmoniously with one another before you put them together in one tank. Putting an aggressive fish next to a smaller fish is a big no no, as well as putting two territorial fish varieties together.