There's nothing more stressful than bad water quality!
I'll tell ya what - I change my tanks like 80%-95% EVERY TIME I do it. I figure if I'm going haul the pump and the hose out I might as well just go big. I have ALWAYS done nearly total Water Changes, with ALL varieties of fish, and I've NEVER had a problem.
BBbbbbbbuuuuuuttttttttttt, mabye my experience is unique, I have heard plenty of people claim that large water changes "stress" your fish. I've also heard that large water changes will damage your biofilter (I call BS on that). AND, the only real concerning thing is I've heard a number of people say that they KILLED thier fish by doing a large water change. So...hmmmm...mabye you shouldn't follow my advice...
But hey it's always worked for me and I hate nitrates.