That isn't a high fish load. If you get them to feed once or twice a week it won't matter that there hasn't been a water change. (I only do water changes every 3 months or so :-? )
I would go to the $2 shop and buy a daily pill dispenser and put the right amount of food for each feed in each compartment then ask your flatmate to empty one compartment in, say, each Monday and Friday or just once a week. Less feeding, less waste, less need for water change.
Hide all other fish food