As a saltwater enthusiast I've always used declorinator with WC. Now that i'm also into FW for a while now w/o any declorinator and there's no effect on my fish that I'm aware of. Maybe because my fish list consist of hardy/big fish such as Giant gourami, arowana, devil chiclid, pacu. I usualy let my the new water sit for 24-48 hrs before using it.