After introducing new fish into your aquarium, it’s essential to monitor water conditions regularly. Test for parameters such as pH, ammonia, nitrite, and nitrate levels to ensure that your water remains safe and healthy.  High levels of ammonia and nitrite can be toxic to fish, so keep an eye on these levels, especially in the first few weeks. See - Testing your aquarium water. It's recommended to perform regular weekly water changes (25%) to maintain water quality. This helps dilute any harmful substances that may build up over time.