Specifically the water you put into the aquarium for the first time you are setting up. Should it be treated/de-chlorinated? If so, do you treat the water when it is in situe or every bucket full you use?
Well the bacteria don't get along with chlorine, so always treat it, how and when you do it, is up to you, but do it before you start the filter and start pumping the water through it.
Duke, there is no reason to differentiate between a newly established tank and one using the fishless method. Either one requires that chlorine be kept at a minimum o avoid affecting your filter's bacteria. Dechlorination is always needed unless you have a long established tank and are doing less than about a 10% water change using chlorinated water.