If you are showing ammonia after a water change, this is likely from the use of chloramine in your tap water. The dechlor will reduce the chlorine, leaving the small amount of ammonia for the filter to take care of. A product like Prime doesn't remove the ammonia but binds it up in a the safer form of ammonium, which the filter then takes care of.
As BBradbury has already stated, don't get too concerned about pH and such or even the hardness, as fish are very adaptable to varying conditions. You do want to maintain as stable an environment as possible, and this is easiest done with regular water changes.
Join a fish club. Don't have one in your area? Start one.