Substrate is way too wet

[JNott]

I've had hermit crabs for a little under 3 months in a 20ish gallon tank with about 2-3 inches of substrate, my humidity and temp were really great up until about two weeks ago when I noticed some flooding. Thankfully both of my crabs were able to go through molting before the flooding, and seem to be adjusting well. They have both swapped out their shells for better fitting ones without issue. I'm getting a new tank on Friday, and will be able to mix in new dryer substrate then. My question is how do I fix the flooding and prevent it from happening in the future? I currently have a small humidifier that I only ever turn on if the humidity dips into the 70's, and was in the habit of just dumping their old water out into the substrate before refilling their dishes...which I probably should stop doing. I'm still very new to this and could really use some advice.

[Hermitsandplants]

yeah dumping the old waster into the sub is a good way to cause flooding, i usually just dump mine outside. i have heard of some people putting a fake bottom in, and i use a thin layer of aquarium rocks at the bottom. i would add more sand so its more around 6". its kinda hard to fix flooding unless you are dumping out all the sand and stuff, so when you get the new tank mix in the wet sand before adding in more water, and keep the consistency about the same as sandcastle sand. hope this is helpful