I would try a .5 or .75 ppm dose of ammonia. Let it sit for 48 hours. If your nitrates are above 3 then do a 50% water change and dose another .5 ppm ammonia. I think your nitrites aren't moving much because we keep getting into feast or famine situations. I'd do your best to try and keep nitrites between 1 and 3 in that tank without starving your ammonia for more than 48 hours between doses, you might lose some but you will keep enough of them to start leveling back up with the nitrite converters.