I believe that the majority of quality water conditioners have an immediate chemical reaction upon contact with water, neutralizing chlorine, ammonia, and a variety of heavy metals. If you follow my method, simply dumping a little conditioner in a 5 gal bucket, filling with water, which mixes in the conditioner, then pour into the tank, you should have no problems.
I change about 50 gal. A week from my display tank alone. That translates to only one cap full
of water conditioner.