Chlorine is unstable it will turn into gas and dissipate from water after 24/48hr. But Chloramine is much more stable and won't dissipate from water quite so easily. So if u have Chloramine in your water you will have to use water conditioner to remove it. An easy way to tell if you have Chloramine in your water is to fill a large white container, bucket or bath. If the tap water has a green tint to it then u have Chloramine in your tap water. it also helps to see the colour if you compare it with distilled water. Another interesting fact i found was that Chloramine is derived from Chlorine and ammonia. Now if your water conditioner states that it removes Chlorine and Chloramine but doesn't remove ammonia. Then your water conditioner will remove the Chlorine in the Chloramine and leave the ammonia behind. So what you thought was nice clean de-Chloramined water for your aquarium is actually tainted with ammonia.

And as we all know even in small amounts ammonia is BAD.