HCA: Hermit Crab Association

Apparently, the idea of having optimal heat AND humidity in my tank are mixing like oil and water right now...

I have a 10 gal. tank with three tiny crabs, using deep, wet coconut fiber substrate (which my crabs LOVE). I tried an undertank heater that didn't work out so well, it dropped the humidity while not changing the temperature much, so I got rid of it. Now, I just put a 25 watt moonlight bulb in there, which is keeping them at a perfect temperature, but the humidity just dropped from 70 to 30 in about two hours. When I turn the heat off, the temp drops down really fast, but the humidity goes back up. I've tried misting in there but it only helps for about 30 minutes. I'd try to put more water into my substrate to moisten it up (it dried out a bit because of the undertank heater), but i've got a completely buried crab who's refusing to come up, and I don't want to accidentally drown him. Can anyone think of any other ideas for keeping these two at optimal?

You should continue misting. Also, I'd keep a container of water in there. It will evaporate and condense and bring up the humidity.

Are you putting the heat lamp inside the tank, or is it above it? What kind of lid do you have? I use a screen lid covered with plexi-glass and have my lights above that; it works pretty well. If you have the light inside your tank, however, it will probably decrease the humidity more.

I would also recommend moistening your substrate a bit, even though you have a buried crab. I've heard that you can stick your finger into a corner of the tank and then just pour in some water, but I usually just pour a little water around on the substrate. As long as you pour slowly and don't put too much water in any given spot, your buried crab should be okay. A few other possible ways of raising the humidity are having larger water dishes, putting the water dishes under your lights so that more water will evaporate, adding a moss pit (I've never tried it, but I've heard it works well), and adding a bubbler. Misting will also help boost the humidity temporarily.

Well, I've got an aquarium-type hood, with tube lights in it, because that was the only way I knew how to get the lights in there to where they'd actually be effective. I've got very large water dishes for salt and fresh water, as well as a sponge for each. Although there's quite a bit of what looks like condensation down where the substrate is now, but the humidity gauge says it's only at 50-55%. Is it possible that the air may be drier, but the substrate is moist enough for them? Or that my gauge is wrong? I don't want to get the substrate too moist in attempts to make the air humid, and invite mold and other nasties in there as a result.

The crabs all seem very happy with their new home from what I can tell, but that could also be because it's SOOOO much better than their old one (the pet store), lol.

Oops, I just realized that there are a few things I forgot to mention! First of all, it's definitely true that humidity gauges are sometimes off, so here is the link to instructions for calibrating them: Calibrate Hygrometer

If your gauge is close to the top of your tank, you might want to move it down a little; it's best to put the gauge only a few inches above the substrate, so that you can get "crab-level" readings. As for the substrate, it should be about sand-castle consistency (or coco-castle consistency, I suppose, if you are using EE ). Basically, it needs to be moist enough that your crabs can make caves to molt in, which in most cases should also help keep up the humidity. You can prevent mold by moistening your substrate in salt-water and soaking your wood pieces, coco huts, etc. in salt water. I've had some mold problems in the past, but most of them came from either my humidity being over 85% for long periods of time, or from my crabs hiding food all over the place.

This thread may also be helpful: Click

well, I figured out my problem. It's the fact that my hygrometer sucks. We had a couple that sit around in our house, and I put one in the crabitat and it's showing up at about 80-85% humidity. I tried to calibrate the hygrometer I had for the tank, but there isn't any way to do that, because short of taking the entire thing apart, I can't access a screw to calibrate it with. But anyway, long story short, everything's fine now. I'll just have to go get a new hygrometer to keep in there.