HCA: Hermit Crab Association

Hey guys I upgraded from a 40gal to a 75gal a couple months ago and I wasn’t having any humidity problems until now. When the weather was colder my parents kept our home on heat and now that it’s getting hot my parents cranked the AC down so it’s a lot cooler in the house now. I’ve noticed that my humidity has gone down for about 1-2weeks now. I have always used a day time heat lamp 60w for lighting and heating their crabitat (humidity would read 75% when turned on) and a “moon glow” 40w lamp that produces their night time with heat (humidity would reach 78-80% when turned on). Also purchased a zoo med uvb fluorescent light bar thing that sits on top of the tank a few weeks ago, I don’t know if it makes much of a difference though since it’s on top of glass and i’m not sure if the uvb rays can shine through or not. It just adds more light to the tank when the daytime heat lamp is on as well. Anyway the moon glow bulb stopped working after a few months and they weren’t using a night time lamp at night for nearly a month (still received the same humidity readings 78-80% without it though). I just now bought another night heat lamp 50w for them. But anyway a few weeks ago before my parents cranked the AC down the humidity was fine (also wasn’t using a night heat lamp at that time for nearly a month). It was 78-80% humidity and temperature always sits at 80 degrees. With that being said I have noticed the humidity drop over the last 1-2 weeks. It’s been sitting at 70% humidity with the daytime heat lamp & long skinny uvb fluorescent zoo med light bar when turned on. Then the humidity bumps up to about 72-73% when the night heat lamp is turned on (also was reading about the same humidity % before I bought another night heat lamp). Not sure if it matters but I keep my tank in my bedroom on a desk with a blanket on top of a glass lid/backside of the tank next to my bed and it happens to be underneath my air vent. I ended up closing my air vent in hopes it would make my room warmer for the crabs. The lid is glass and is fully shut as well by the way. I have 3 small UTHs on each side of the tank (I put styrofoam on top of them and taped it down ~ haven’t had any problems). I still plan on adding much larger UTHs that cover the entire walls of the tank.
I know that was a lot of info and i’m sorry if it was confusing but i’m awake at 4am typing this because this has gone on for about a week or two and I believe my crabs are acting lethargic. The crabs were fine until the humidity dropped it seems like. They were always out and about and climbing & more. Now they sit by the heat pads for hours and it makes me sad. I hope they aren’t suffocating or anything because lack of humidity. I haven’t even seen them go in their food bowl for the past 4 days and one of the crabs LOVES to sit and hang in the food bowl, that’s all she does. Now she’s not very active and she’s the most adventurous one out of the group who aren’t molting right now. (P.s the crabs who are burrowed have been making a lot of ruckus all day and night)






my digital acurite reader stopped working unfortunately, I guess it was because I kept it inside the tank. It starts to work barely after being left outside of the tank for hours. I also have a little random digital temperature reader with a probe placed down into the substrate. I know the non digital readers shouldn’t be counted on for accuracy but thats what I have right now.


Sent from my iPhone using Tapatalk

okok I may have bumped the humidity up to 73% i misted some of the stuff in the tank that supposedly help with keeping humidity levels high. one of the crabs left the heat pad after being there for hours.


Sent from my iPhone using Tapatalk

I know it's tough getting supplies with everything being shutdown, but when you can, I'd get the largest uths you can find to fit the different sides of the tank (not sure what sizes you have now). A lot of people on here recommend Ultratherm. Your heat lamps are probably zapping the humidity. I can't remember, do you have any air bubblers/stones in your pools? From what others have said, that can also help raise humidity levels.
You're right about the UVB rays and the glass. The glass is likely filtering them all out. So if it ever burns out, you could probably just get a regular light to replace it.
I'm sorry you're having issues! I know you love your crabbies!

Sent from my Moto G (5) Plus using Tapatalk

It is always difficulty and frustrating trying to tweak everything in your crabitat on the fly. The first thing I would do is make sure to calibrate your gauges to be sure you are getting correct reading. That way you you aren't getting in a panic over gauges that are off a little bit. It is also the least expensive options.

Calibrating a Hydrometer
viewtopic.php?f=26&t=92540

The other thing I always like to do with new tanks is move the gauge around to several spots in tank. High-center-low, front-center-back, Left-center-right. They can all be different. I know in my 75 gallon readings can vary 20 degrees from the rear glass to the front. Larger tanks tend to have a greater variance due to their size. Once you get everything just right they also tend to be less work maintaining.

I'm not a big fan of many heating aside from Under Tank Heaters. I try to avoid them since they are notorious for drying out the substrate more.

When you purchase a new UTH I highly recommend an Ultratherm 11X47 from Reptile Basics. They cover the rear of a 75 about perfect.
https://www.reptilebasics.com/ultrather ... th-11-x47/

Also it would suggest insulating the UTH once it is installed. Reflecix is a great easy product to use. It reminds me of an aluminum bubble wrap. they have plenty of roll sizes at home improvement stores.
https://www.reflectixinc.com/products/d ... nsulation/

If that still isn't enough you can also insulate one or both sides of the tank as well.

Depending on how your tank reacts to the changes you may actually need to lower the temperature. Thats when you can add a thermostat to your UTH. They won't raise the temperature only cool and maintain. We use an I-Power brand off Amazon. It's inexpensive under $20 and have not had any issues with the 5 or 6 we purchased for our tanks.
https://www.amazon.com/iPower-40-108-De ... _s_sparkle

Just for me to to try and cover everything thoroughly to avoid any issues. Be sure the UTH's you have insulated are the type that are able to be insulated.


Hopefully that helps you out. It's a lot of information at once. Take your time and work on calibration and placement of your gauges first. If you have anymore questions feel free to ask.

Good advice given, I won't add anything to it. Except that most of us don't measure the temp of the substrate. Can you use that thermometer at surface level?