With FW I have never had a problem. I do 50%+ weekly waterchanges. For filtration, I only run a Rena XP3, on a 120 gallon aquarium. But for my FW angel tank, which is 29 gallons, I run a penguin 350, which is more then 10 times the volume moved per hour. The more flow the better the fish seem to do, and even angels can adapt to a strong flow, as long as it is a wide pattern, not a tight pattern.
SW on the other hand I have had more losses, but that was due to acclimation, not water quality.