I was trying to put a picture but at the moment my crown is stuck and can't open the coil out. anyways, my coil (ni200) is brown but the cotton is still very good. This happened to all the coils that came in the box, .5 and .25. I ended up tossing them because they didn't wanna work out anymore. I heard these could last pretty long from what I've was but I can't get the brown on the coil cleaned. Anyway I can prevent this or fix ?? Please help