HCA: Hermit Crab Association

So I recently upgraded to a 20 gal tank I have everything for my hermit crabs to survive but unfortunately I can’t keep the humidity right I have moss soaked in fresh water, I spray the tank, I keep salt and fresh water available at all times, the temp is usually at 75 I have a under tank heater on the back and when it gets colder I have a night time spot light. I have a daylight light and press n seal literally have tried everything. The humidity doesn’t budge from 69 and I am so worried about them dying. I am thinking of getting another uth and removing the spot light but idk if that will help. Even with a uth and spot light the tank is only 75 but the humidity is always in the 60s I hope someone can help me.

What kind of humidity gauge Do you have? Analog gauges need calibrated and even then are notorious for being wrong. Many here use accurite that can be found at Walmart. I have a zoomed temp/hygrometer. I’m not ready to recommend the zoomed unless I could compare it to another digital gauge.

My pools have just enough surface agitation with filters that it keeps the air humid and my lid is not air tight. Your situation might need a tight fitting lid and or an air stones in your pools. Also there’s a diy humidifier on this site somewhere. Be aware of any splash out created by air stones or power filters. That can cause flooding.

Is your substrate moist? Sand castle consistency. It should never be completely bone dry. If it’s dry your humidity will always be a struggle. The surface can get dry and that’s ok. As a matter of fact I’d rather see my surface dry out once in a while. I used to have to mist my sub on occasion but not anymore. My surface hasn’t been drying out but that maybe because I stoped using a small fan I have in the tank.

I also use a blanket over the top of my tank mainly to hold in heat. I also have it draped over the front glass to keep condensation at bay. My fan used to keep it at a min but that’s turned off. My heater is a bit small. It doesn’t cover the entire back like it should, at least from the sub surface to the top of the tank. So the blanket held me a lot. If I want I can let temps go up higher than 85° when my lights are on. But I have my thermostat set on 81 and the sensor is in the coldest spot of the tank. When my lights go off the temperature will gradually drop to 77-78°. I also fold back the sides of the blanket to allow the gap in my lid to be exposed if I don’t do that my humidity gets too high which is not an issue for the crabs but could be an issue for flooding. I tried to never let my humidity fall below 80%. The only time it does is when I open the lid to change water and food.

I hope I helped at least a little

Deep, properly moist substrate, solid lid, and moving water.

Turn your water sources into bubble pools; this makes sure they have fresh air pumped into the tank on a regular basis, and generally helps with humidity (I have heard that if you live in desert-dry conditions, it may not help). The thing that boosts humidity best by far is using a fountain in the tank, if you can find one with a good "pool" feature at the bottom to allow them to submerge. Also, live plants in the tank are AMAZING for humidity. Pothos is super easy, will eventually climb all over the tank once established, and creates natural foliage to help them feel more at home and hidden.

Just realized this is a double post.
But... I tried pothos in the sub and moss tied on wood. The moss can hang in there but not spreading as I suspected. I’m not going the water it all the time. I use a spray bottle set on one stream so I can direct the water to the moss only but some splash does occur. I’m not going to keep watering it like that and cause a flood.
The pothos started dying so I pulled it all out. But it was sprigs I had rooted in a jar of water and I just shoved them into the sub. Must’ve been too big of a change. Since then I’ve been pondering how to grow pothos or something in there. Not trying to hijack but any help on the pothos is much appreciated. I’ve thought about trying to just set a pot in there.

Edit: I’m using filters in the pools and have had second thoughts ever since I switched from air stones (bubblers) since the air stones add some outside air.

I struggled with humidity in my tank for a while, the only thing that helped was getting a plexiglass/acrylic/glass fish tank lid for the top.

I always have at least one of the pools with an air stone as a bubble pool. (Either both like that, or the MSW pool is a bubble pool and the fresh water source is a fountain.) I do think it is important to get fresh air pumped in on a regular basis. I have the air pump on a timer so I can adjust how often and for how long it runs (I also always have a small fan in the tank, and it is hooked to the same timer, so it runs whenever the water is moving). Having air pumped in at substrate level, and a fan running in the tank, also makes sure that the air is stirred up down there (CO2 is heavier and tends to settle without air movement). Having a fan in the tank also is the only thing I ever found that would prevent mold growth.

As for growing pothos in the tank, I had a very happy pothos plant that grew all over the place in my 55g. I started it in a small terra cotta pot, which I blocked the hole in the bottom with a cork sealed with aquarium silicone (so when I watered it, it would not cause a flood). Once it was growing well, I put it in the tank, sunk down into the substrate. The terra cotta pot allowed the water from watering the plant to slowly diffuse into the surrounding substrate, so that was an additional plus. But you could use a plastic pot the same way. I protected the plant from crabs digging into the pot and injuring the roots by fastening a plastic grid over the top of the pot, with the main vine growing through a central hole.

I think others have had pothos just growing in the substrate, but for me, I think protecting the roots was important (because I had first tried just putting a pot down in the substrate without a grid to keep the crabs from digging in the pot, and they just kept digging down into the pot, disturbing the roots). Also, if you have used some amount of saltwater to do the initial moistening of your substrate (which most people do), salty soil is hard on a plant (will kill most plants). Pothos is pretty tough, but trying to grow in salty soil AND having your roots dug up regularly is probably too much to ask, even for pothos!

If you started a (very large!) tank well ahead of time without any crabs in it, and used very little salt water to moisten the substrate, you could probably get the pothos growing strong, vining around everywhere, and setting down lots of roots everywhere (my pothos did vine around and set down new roots outside of the "home pot"). If you let those establish for a good long time before putting any crabs in, and only had two or three crabs, you probably could keep it that way, because the crabs will tend to find their preferred burrowing locations and the little contained ecosystem could balance. But even then, having a "home pot" where the plant originates has a lot of advantages--for one thing, if you do need to (or want to) redesign or do a deep clean, a "home pot" would make that more manageable.