Well I can't say I know its mold for sure, but I think it is. I hit my DBV through my beaker bottom bong and even with a few screens tiny bud particles get through and even though i keep this thing really clean they will stick to the edges and turn white. So after a few days of use, even though I change the water at least once a day, the bong will have lots of white spots above where the waterline would be. They are hard to get off and I figured they are just bud particles that stuck and had their color bleached out into the water over the day. But when I leave water in the bong overnight or over a day it does have a moldy smell. And my friend commented and said "Is there mold in your bong?" Does anyone else get this problem or am I doing something wrong?