Chlorine will break down in sunlight or on exposure to atmoshere, if I recall my basic chem( I suk at it) Usually 24 hrs thit ariation will drive most of it off, but as stated it wont deal with chloramines or some of the other nasty stuff added to typical mun water supplies.
For a swim tank( fish only) adding a basic neutralizer and airiating(sp) will prolly do the trick, but for reef dwelling inverts its false economy to not provide the best source water possible(ie RO/Di and good salt mix). Most of the time tap water in a reef tank will result in probs somewhere down the road
