right now go for 30%-40% every week or so don't go more the 2
when they get bigger go for more like 50%-60% a week RTC need clean water and oscars make water dirty fast so you'll need to do big water changes
WATCH you balas and oscars both will be out grown eventuall the clown knife better grow fast if it hope to not be eaten how big is it now ?
do a 50% water change weekly and add one TBS of salt to 5 gl.
but your fish inthe tank may or may not do this TSN eats knife and your RTC eats the oscars and bala and the knife and TSN so be on the lookout