I'm relatively new to vaping. I bought a couple MVPs and a couple Protanks. The first time I topped off the tank the new liquid turned dark and tasted burned. I ended up dumping the liquid, and replaced the head. I just filled the tank and screwed it onto the MVP, and it won't fire. But, the light stays on for several seconds. It normally shuts off as soon as you release the button. I put the tank on the other MVP to see if it happened there as well. It did. Can someone please help? Thank you!