When to pull the plug/restart?

[gobytron]

I'm lazy.

I'd run carbon, maybe some Chemi Pure.

If you don't know for sure what got in there, it's tough to do much more than try a blanket solution.

If that doesn't work, how hard is it really to redo a nano?

You probably have a stash of new sand and LR (don't we all).

Then again, this comes from a guy who never feeds or does water changes.