Here's why:
* Ammonia is toxic to fish. Even low levels can cause stress, damage gills, and lead to illness or death.
* The nitrogen cycle needs to be established. Ammonia is a byproduct of fish waste, and it needs to be converted through a process called the nitrogen cycle. This process requires beneficial bacteria to turn ammonia into nitrite, and then nitrite into nitrate, which is much less harmful.
* New tanks don't have established bacteria. When you set up a new tank, it takes time for the necessary bacteria to colonize and start working.
Here's a safe approach:
1. Cycle your tank before adding fish: This means allowing the tank to run for several weeks with a source of ammonia (like fish food or ammonia solutions) to encourage bacteria growth.
2. Test your water regularly. Use a liquid ammonia test kit to monitor levels.
3. Only add fish once ammonia levels are consistently zero.
Remember: It's better to be patient and wait for your tank to cycle properly than to risk the health and lives of your fish.