Smaller changes weekly are better than larger changes less often for a tank that is properly stocked. The more frequently you change a little water ( I recommend 10%- 15% weekly), the less likely your water chemistry will get out of whack and hurt the fish. (Fish do not like change! unless it's from bad water to good and even that can kill a fish if done too quickly.) I've been keeping tropical fish this way for over 40 years and I don;t have many of the problems with my fish or tanks that I see posted on this site. ( Just sayin'
Hope this helps