Yikes Mold . I cant imagine that is a very nice thing to see in your drink bottle. I have had my bottles since I got my bike about a year ago and I dont have any problems with mold. I make sure that I remove my bottles from my bike as soon as I'm home and wash them out. I leave them on the drainer until they are completely dry and then pop them away until my next ride.

Im with Grog - if you see mold I think its time to get some new bottles.