Okay, couple things folks. The toxicity of chlorine/chloramine is proportionate to the amount of water...if you put less than 10%, the volume will dilute the chlorine into harmless concentrations. Chlorine is BAD, there's a reason they use it as a poison gas. Don't force your fish to tolerate it... I always add conditioner when I'm doing WCs, I add it to the tank right before I start filling.
RO water is terrible for freshwater tanks, and Di/RO (de-ionized) is even worse. Why? Because it has no buffer, no minerals...using pure RO in freshwater is asking for a deadly Ph crash. If you need really pure water of lower mineral content, like for rays and discus, usually you mix 50/50 with tap water.
Marine is a different story, tap water is full of nutrients and chemical crap that may cuase algae blooms and other issues. Your salt mix contains the natural elements that re-buffer the water.