Good morning M...
I change a minimum of half the water every week in my 55 G tanks. If you could ask the fish and plants how much you should change weekly, I bet they'd all say "The More, The Better!".
The more clean, treated water you run through the tank, the heathier your fish and plants will be. That's because if you're always flushing new water through your tank, there's no way for wastes to build up before the next water change.
Your water will stay clearer too. The water in my tanks gets a little cloudy after a water change, because the gravel is disturbed, but I have an extra power filter I use. I just put a little polyfiber in the media reservoir and run it for a day or two and the water clears up.
The water clarifier is pretty harmless, but I never put chemicals into my tanks. The extra power filter will do the trick without the clarifier.
B