All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. Before adding bacteria or fish to any aquarium or system, all chlorine must be completely neutralized. Residual chlorine or chloramines will kill Nitrifying bacteria. Most US cities now treat their drinking water with chloramines.
Chloramines are more stable than chlorine.
It is advisable to test for chlorine with an inexpensive test kit. If you are unsure whether your water has been treated with chloramine, test for ammonia after neutralizing the chlorine. You can also call your local water treatment facility. They are made by adding ammonia to chlorinated water. Since dichloramine has two chlorine molecules, a double dose of a chlorine remover, such as sodium thiosulfate, is recommended.