fishhead's issue sounds like a case of operator error. See quote below.
If what he states is true his fish are all being subjected to chlorine/chloramine while the tank is filling, right up until it is full. For that reason I treat (approx. half dose) just before adding tap water, and again (approx. half dose) near the end of the fill. (approx. 3/4 full tank)
As I have pointed out numerous times over the years, unless one knows their disinfectant residual levels as they leave their taps, how much dechlorinator one uses becomes a case of by guess of by golly. Manufacturers generally only recommend a dechlorinator dosage rate based on a specific disinfectant residual level. That "recommended" dosage rate is only a baseline quantity based on a specific residual level. In the case of water conditioners one size does not fit all.