Yeah, I suggest watching the parameters, doing another WC, and then watching the parameters some more. If the nitrite isn't going down you've got a dead fish wedged in your rocks, and if it's the sixline you'll prolly never find the damned thing. But if you've removed the problem, your biological filter should get rid of the nitrite pretty quickly. I'd also stop feeding for a day.
Do you have a brittle star in the tank? I highly recommend these, they're excellent scavengers.