I know that if I change 100% of the water, I used aged (1 day) water and have no problem. The one time that I changed 75% of the water using fresh mix water, my coral all stressed out and a few mortality resulted, including fish. Everything was disolved and the water was clear and well oxygenated. I did not try to use freshly mixed water after this event.
There are plenty of reading material over at the Chemistry forumn at Reef Central on this topic.