I agree with what has been said about feeding. I feed my fish once a day and that is it.
Also, like Coralmushroom pointed out, a 2 inch sand bed really isn't deep enough for good denitrification to take place. It still will, assuming the sand bed isn't disturbed by vacuuming, etc.., however to get any real effectiveness here, a minimum 4" DSB
In lieu of these items, there are a few other things that can be done. Protein skimming and running GAC
will help remove DOC
's from the water. The less DOC
's available to break down the better as this will slow the nitrate increase. Also, growing and maintaining your own algae (as in a refuge) is a great way to keep nitrates down. Most people who have fuges plumbed into their systems have a reading of 0 for nitrates. There are also a few products on the market that claim to remove nitrates from the water. Seachem's Purigen
are examples of these types of products.
I hope some of this helps. Unfortunately without some type of actually removal process for nitrate (water changes alone wont' do) nitrate will continue to climb on an upward graph...