Nitrites are converted by bacteria into nitrates- it's these nitrates that the plants use. Plants won't thrive in your filter, but you could get some duckweed for your tank- it spreads quickly so there will be enough to soak up some nitrates as well as feed the fish.
If its actually the nitrites that are high, you just have to keep doing water changes to keep it at a safe level (preferably zero).
Make sure you aren't destroying your bacteria by over cleaning your filter or cleaning it with untreated tap water.