Whats the buildup on my Nzonic mod magnets? Its black and and causes my mod to not fire properly everytime. How can I fix this? And could the battery be a problem?
If this is tarnish... don't sand nickel plated magnets. Depending on the quality (this a clone?), the plating can be very thin and overly aggressive use of even a fine 1000 grit can remove it. Instead, use a pencil eraser... or ink eraser if the tarnish is heavy.
If the battery is old or of low quality, there may be enough internal resistance where, when used with sub-ohm builds, you have heat (joule or resistive heating) being produced.