I used the handle of a wooden spoon, and pushed it down into the substrate up against the glass where I knew there were no molting crabs. I couldn't push it all the way to the bottom, but I know it was very close, maybe 1/4 inch from the bottom of the tank. I then used a light to look down in the hole. I didn't see any water accumulate in the hole, even after a few hours so I guess that is a good thing.
I can see about an inch of the bottom of my tank because it is a bit bigger than my stand (I will be moving it to a bigger one soon), and for the most part the substrate looks well mixed, just like the rest of the tank, but there are some pockets that appear to just be sand and it looks like wet sand. Should I be concerned about this?
I have at least 6 molting crabs right now so I would hate to have to dig them up if my tank is flooded. The only ISO tank I have is a 10 gallon and I have 11 crabs so that would be a problem.
Here are some pictures looking up at the bottom of the tank. I also noticed something in the right corner. Does that look like it may be a crab (3rd picture)?



