It's hard to tell by the single picture but if you have a puddle of water under your substrate this COULD be the start of some minor scale rot....I'd be willing to be that's what you're dealing with considering the standing water. You should be actively monitoring your humidity. If you have standing water in your enclosure that probably means your humidity levels are off the charts, which is not a good thing. As CALM says....it's also a recipe for bacteria. Warm conditions + standing, stagnant water = every bacteria known to man
It helps us greatly to post temps in Fahrenheit however as most of us are from the US and would prefer not to have to go back to Google for a conversion.