I posted the following last year, some of you may find it an interesting read.
http://www.monsterfishkeepers.com/forums/showthread.php?309623-Cost-Effective-Water-Conditioners
Cost wise, for my local water conditions, Seachem Safe came out the winner.
I use NO conditioners. What for? Before I give my fishes water conditioners, I'd have to set myself up with some pure Oxygen for the house.
Hey whatever anyone does is fine, Heck, some people feed their dogs Filet Mignon. But I know a lot of reputable Vendors and MFKers that dont use any extra or special chems.
If you have to ask "what for?", then clearly you do not understand the toxic effects of both chlorine and/or chloramine on aquatic organisms. At lethal levels both will kill fish by internal hypoxia via gill damage. Even sublethal levels can cause moderate gill hyperplasia.
In simple terms, these chemicals burn sensitive gill filaments, causing the fish to slowly suffocate.
The acute toxicity of both chlorine and chloramine to aquatic organisms is species specific and is dependant on the chemical species and levels, life stage of the fish, exposure duration, pH and temperature.
Certainly some people can get away without using any form of water conditioner, usually due to the fact that the disinfectant residuals coming out of their tap are non existent.
From what I've seen & read over the years, the vast majority of fish keepers have no idea what those residuals may or may not be, and the entire "water conditioning" process becomes a
by guess or by golly approach. They could be using 1/2 as much Prime etc as they should be, or twice as much as required, to treat their local tap water. The instructions on water conditioner containers are simply guidelines, based on various residual rates.
Obviously someone with 4 mg/l chlorine residuals at their tap is going to have to treat their water changes differently than someone with .5 mg/l (or less), just as those who have chloramine residuals to deal with, and who may perform very large water changes. At higher pH values the resulting spike of free ammonia once the chlorine/ammonia bond has been broken in chloramine can also have a very negative effect on the health of a fish, even in small doses over an extended period of time. Just as disinfectants, free ammonia is also highly toxic to fish.
All of the above has been very well documented for decades, with numerous species of fish at various life stages.
