fish food

i have a 4" red festae.. he eats frozen prawns most of the time. the other day i tried putting in other foods to see if he would eat it. i'd put a rice bubble cereal in.. and he would smash it.. then i'd put some noodles in.. he would smash and gobble that up too.. then i put some macoroni in and he would smash them too.. he seems to love all these carbs.. my question is.. would this be ok for him ? would it stuff up his digestive system or anything? would this affect the water quality etc. i still do my regular water changes..

thanks

regards

robbie