In reference to the ammonia build-up in the FT.. I've read that some people do a 50% change on their water every once in a while, is that because the water has built up to a point that the plants can't keep up?

I've also read that getting oxygen in your water helps break down the ammonia; would it help to run the aerator 24x7, or would that be overkill. And as a side to that question, is it ok to only run the aerator 15 minutes on and 45 minutes off, or does the change in noise hurt the fish at all?