HCA: Hermit Crab Association

I couldn't think of a better term of it.. "watering your substrate" sounds kind of strange, doesn't it?Anyway, in previous tank iteration, I had decided to try to keep the substrate moist, because I thought it would make digging/molting easier, and also keep the humidity up, counteracting the 115w of lighting I had.I would pour roughly 2-3 cups of water into the substrate each week (sprinkled around, not all in one place, kind of like a bi-weekly rain shower). Note that I have a 92g tank, so 2 cups doesn't go as far as you think.As I'd reported on in the past, I didn't have very good success that time. I think oversaturating the substrate may have been one of the issues.So for the last 6-months to a year, I've mostly stopped. Maybe once every 2 weeks I'll give a cup of rain, but that's it. Not bi-weekly anymore. I really think the crabs are more than capable of moistening and digging and molting in drier substrate. And I think the less-moist substrate is safer than saturated substrate. Since we don't have real-world circulation and filtering, bacteria and chemicals can build-up easier.

JMT, I was perusing through the archives yesterday and I think I confused myself. I have a 10g with a mixed substrate (coco-fiber and sand). I occasionally do the finger-hole thing to keep the substrate moist and add humidity (maybe 3 times in the 2 months I've had it). I'm comfortable with that (sounds similar to what you're doing). Should I 'mix-up' the substrate occasionally, as well? I don't think I've seen a consensus on that. I've heard of removing the top 2 inches, I've heard of stirring the top 2 inches, or perhaps stirring up a deeper portion? (I don't mean to imply that these questions are solely for JMT, only that I certainly appreciate his experience.)

it only "rains" when the top layer of sand seems to be getting too dry (with a heat light) and that's only as much water as it takes to dampen it back down. (it varies) maybe a cup, sometimes less.

The finger-hole method is used for maintaining humidity. It gets the lower substrate moist so that it keeps the humidity up for weeks, rather than hours. You don't have to mix it up, becuase the hole gets the water to the bottom layer already, and that's where it should stay. I have a UTH on my ISO, so the UTH half stays dry, while the other have stays moist.I'm not sure about stirring. From a substrate health measure, stirring should be performed. But I think that it could be detrimental to buried crabs. So I've never done it. I've done the partial substrate change, where I scraped off the top layer of substrate and replaced it, but I was very careful in removing the substrate and adding, so as to not apply pressure or overly disturb any buried crabs.In my situation I was referring to in this post, my humidity was already high. So the "watering" was above what was needed to maintain humidity. I was even keeping the top layer moist. And if the top is moist, the bottom might be damp. A fine difference. Moist is OK, but damp could breed bacteria.So that's why I'm recommending just enough water to keep the substrate moist, but not damp, and if the surface is dry, that's not a problem. If you need to add water for humidity, just add enough to provide the desired 70-75% humidity level (remember humidity will be higher close to the surface, while the gauges are probably mounted higher), and don't saturate the substrate by adding too much more after that.But an occasional rain shower isn't going to hurt them. Just not regularly so it ends up staying too damp.