HCA: Hermit Crab Association

A few days ago I finished setting up all the furnishings in my new crabitat, and have placed a couple of humidity gauges around different areas to check how things are doing in there. On the substrate, the humidity stays pretty consistently between 80-805%, but on the second level, which is about 6 inches above the sub, humidity was at 60% when i placed it in. I hoped it would increase as it circulates, but now the humidity at the substrate increased from 80 to 83 but the humidity at the second level dropped down to 55%. Any ideas on how to make it more even throughout the tank?


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Bubblers and moss pits are known to help, as well as decreasing ventilation, possibly through placing a wet towel on top of the tank

This really isn't something to be too concerned about honestly, the humidity and temperature are going to be different throughout the tank and the crabs will move to where they're most comfortable. Relative humidity will read lower if it's warmer as well.

So as long as the humidity is fine at the substrate level, they will be fine if its dry up towards the lid? Will be interesting to see if they avoid hanging out up there for long.


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I definitely wouldnt worry. I recommend you calibrate the sensors, unless you have a lid that holds no moisture I struggle to believe theres a 40% difference between 6 inches.
As was previously mentioned, tho, gradients are rarely if ever a bad thing. Nothing is perfectly even in nature, and creatures are smart enough to go where they’re comfortable. Admittedly humidity gradients are a little iffy when it comes to gilled invertebrates, but i still believe it should be fine. It gives them options and choices to go where they want to and get what they need in any given moment

Well is the gauge directly on the substrate? like, touching it? It's usually recommended to put the gauge a few inches above the substrate because putting the guaue too close to the sub will skew the readings. I mean think about it, you're putting the gauge on water. So, if the bottom guaue is on the sub or almost touching it, I'd say that reading is inaccurate. You wanna put your guaue a few inches above the sub, and see what that reads.

ps tips for humidity
- bubblers in your water pools
- water pools near the heated side of the tank to increase evaporation
- wet moss pits (check them occasionally for mold)
- removing most of the ventilation (this should most likely be done anyway)
- putting a decent spread leaf litter and other botanicals on top of the substrate (great food source and holds in moisture)

Thanks for all the advise! I added a couple more moss pits and reduced the ventilation a bit and I am no longer having as big of a gradient, levels are much more within healthy range. I think my lid was letting out too much moisture.

Everyone is moved into the new tank now, so far no problems.


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awesome! glad they're doing well