thio-Sulfate ions dechlorinate water, S2O3 --, I am not sure what state sulfer has in ground water. The other dechlorinators have an " S03-" end to them for the same reaction.
What about a de-ionizer or reverse osmosis set up? Are you sure your water is bad for fish? Wish I knew something about iron, sulfer and fish, but I don't. You say sulfer leaves the water? Then I would think that aeration would speed that up, so that you can make water ready by putting it in a holding tank (aka clean plastic garbage can) and run an airstone in it overnight. Might as well toss a spare heater in there too, to make it tank temp. But I would think only a de-ionizer or reverse osmosis would remove iron. What about those dechlorinators/conditioners that claim to remove heavy metals?