do you have a sponge filter that you've used in your DT, either on a return pump or a prefilter for an overflow?
if so, i'd take that sponge out and put it over one of the intakes of your filters. may give the bacteria the boost it needs to get rid of your nitrites. trates, if you're really worried about them, i'd grab a clump of chaeto, grab a rubbermaid container (clear with a lid) cut some big holes in it, and hang it over the side of your tank, sorta like an intank fuge. make sure it has light and some flow.