So today I noticed a that a small section of my sub is a different color than the rest of it. My sub is 50/50 playsand and eco earth. It's 7 to 7.5 inches. The discoloration is under the food dish, which I change everyday to every other day with both fresh and dried foods. If the crabs happen to make a mess, I spot clean. If I find mold, I usually remove it asap- if it's on the surface of the sub, I just scrape it off completely and dispose of it. This is a completely different scenario
It looks as if something is spreading underneath the sub (with the very top layer looking perfectly fine), and it's mostly yellowish (with a little green on the edges) I haven't detected any odd smells coming from the tank. I've never experienced anything like this. Temp is usually 80-85, humidity is always at least 85. I only mist the very top layer of the sand when it dries out a little, otherwise I try not to oversaturate. The weird thing is that I never mist underneath or near the food, so I'm not exactly sure how this came about. Could it be mold? Flooding? I currently have two molters down. I don't think anyone is near or around the food dish so it might be safe to completely dig out the section, but I'm not sure. Thoughts? What should I do? Here's a picture, sorry for the glare!
be careful not to push down on the dirt. Use a spoon 
messy crabs!!