First -- I'd recheck your parameters. At that much nitrite, you should see some distress.
Second -- in addition to water changes, add an air stone as nitrite affects oxygen intake for the fish.
Third -- You can move media from an established tank and just throw it in the existing filter or even squeeze gunk from sponges in an established into the affected tank.
Fourth -- The careful use of Prime directly into the water can temporarily knock back nitrite.