- Check your water parameterparameters, it should have 0 ammonia, 0 nitrite. Some nitrate presence is not lethal as long as itsit's within the limit.
- Match the pH and temperature depending on the species you plan to put it.
- Water should not be cloudy.
- There should not be any bio-film forming on top of the aquarium. In this case it forms, increase surface agitation.
- Make sure your tank has enough filtration to support the bio-load.
- Tank decoration should match the requirement of the species. Some prefer less open area and more hiding place, some prefersprefer the opposite. Some prefersprefer plants, some prefersprefer rock, some prefersprefer a piece of wood.