Chloramine is way more toxic to fish than chlorine. I was just reading up on it and it says it won't disappear naturally no matter what you do, only way to remove it is to use a water conditioner. Easiest way to know if your water contains chloramine is to test your tap water for ammonia and if it contains some more than likely your water treatment plant uses it instead of chlorine. Or you could just ring them, by law they have to tell you what your tap water contains.