Water conditioners are used for dechlorinating tap water. Everybody has to try products until one is found that is economical and works for their individual situation. Because I am an information junkie I went looking for comparisons between products and stumbled onto THIS PAGE comparing several brands of water conditioners. This page brings a lot of information together in one place and allows the hobbiest to make an informed decision on products to try. After checking out that page cruise the rest of the site for more useful information.
By far the most widely used water conditioner in the Betta hobby is Prime by Seachem. It will take care of chlorine and chloramines. It can be doubled if needed to control an ammonia spike. For this reason it is good to use in spawn and grow out tanks. Prime will also remove heavy metals and give water and aged feel almost instantly.