Hydro Homies

Scraping plastic can cause micro abrasions that allow for mold and other micro organisms to thrive. These can also form from just wear and tear.

Probably the best thing to do is simply to replace the bottle or maybe the cap can be replaced.

This is one of the reasons I try to avoid plastic/acrylic in my water bottles. But if i cant avoid it I try to opt for polypropylene and then just avoid getting it hot.

I can't answer your question, but this is an amazing abstract photo. Would you mind if I painted it?

What you've got there is black mold. I've never run into any that won't come off with hot water, soap, and scrubbing, but I've read in articles that vinegar works to help remove it. The best way to prevent it from happening again is simply to wash your bottle frequently and to let it air dry after washing it.