I bought 2 pro tanks as a new vaper, because I don't want the hassle of having to worry about the content of my liquids destroying tanks. That said...I saw on Grimmgreens site that pro tanks have been reported to have metal shavings in the tube. I used a cotton swab and there were several metal shavings in both of the tanks I got. On one of the tanks, I had been vaping within the voltage guidelines that came with the tank. I let the tank get about half empty when I went to refill it. When I tipped the tank back over after the refill, there was a lot of carbonization in the liquid, which ruined the full tank of liquid. It tasted burnt and foul. I dumped it, and having also bought 4 boxes of replacement heads, I switched that out. On the new head, the coil wire hadn't been clipped properly and were making contact with the outer wall, which I believe is a short. I'm new..so it wouldn't work. After finding the problem and clipping the coil it works fine. I hope that these troubles are rare. Because I actually love the way they work, and taste. If you have pro tank please clean it thoroughly before using it. I would hate for anyone to inhale metal shavings.