I would do larger water changes. There was an article somewhere (I can't seem to find it) that stated you don't start to effectively reduce nitrates until you change about 50% or more of the tank volume. It makes sense, though. If you have a tank that has a set amount of nitrates at a given time, the more you dilute it with clean water, the lower the concentration will be immediately after the change. If you are already committed to doing frequent changes, the extra 20% of water you remove won't add that much time.
Plus, reducing your feedings will help. I've seen several talks from successful fish keepers over the past year or so who only feed adult fish 4-5 times a week.