That is why Pythons make me want to pull my hair out. You are doing it the worst possible way. You are introducing chlorine into your tank and filter. I am going to take a gander in saying that you probably don't own a chlorine test kit, right? Not to worry, because you can call up the water department and ask them what they put in it. You need to know if they put chloramines or ammonia in the water. Your LFS can answer that too.
By adding untreated water to your tank, the chlorine is not only stressing your fish, but it is also taking its toll on your bacteria colony. A slight improvement would be to add the declor before you add your water. But that is like the difference in shooting yourself in the foot or shooting yourself in the leg

By treating the water before adding it to the tank, you allow the declor to do its job.
And if your water has chloramines in it, adding regular declor will release the ammonia into the water. Amquel Plus and Prime will remove chlorine, chloramines, ammonia, and reduce the toxicity of nitrates and nitrites.