I would say it is the start of some type of mold. But that is the problem using the half logs as hides in an environment that requires humidity. Reptile Basics sells plastic ones of various sizes and they work great. The prices are very good as well.

I am not to sure about the coconut fiber for BP. I use Breeders Choice and have no problem at all. If the tub is a little drier then it should be I just spray it down a little. Humidity and temps are always a fighting battle. If you have a rack system two tubs will be just right then you check the third one and the temp is lower and humidity is high. UHG! What to do now? Something will always come up. But that is what makes it so much fun