2nd hand exo terra water bowl - how to clean?

  Hi I just bought a second hand exo terra water bowl and its got black/green patches on the bottom - especially on the edges. What is this and what's the best way to get rid of it?

Thanks for your help.
Sounds like mold.



just boil some water amd put it into it for a few hours ... this will kill any thing on it. give it a good scrub also