HCA: Hermit Crab Association

I bought a temp and humidity gauge that stick on - where is the best location to put them in the tank?

It's best to place them away from the UTH and the pools: having the gauges too close to the heat source will show only the highest temperature in the tank and too close to pools (especially those with bubblers) will give an overly high humidity reading. It is recommended that gauges be placed fairly close to the the ground to get an accurate reading where the crabs actually are. I have a digital Acurite unit that stands on the substrate toward the front of tank, away from both the UTH on the back and the bubbler pools on one side; by placing it there, I get the cooler temperature/drier humidity readings -- if they are within the "safe" range, I know the rest of the tank is warmer/wetter.

oh stands in the tank?? can you link me to it so I can see it please?

Because temp and humidity can vary from place to place in the tank (even in a 10g), I always encourage using several gauges in different places. If you only have one set at the moment (or even if you do have more), here is my suggestion: don't stick them to the tank wall itself. Stick them to longish things that you can use to set them up anywhere in the tank that you want to check the temp and humidity.

If what you have are the little round gauges with round velcro attached to the back (cheaply available at PetCo, for example), then what I do with those is take old round chopsticks from Chinese takeout and put the thin end of the chopstick up through in between the two kinds of velcro (leave the paper covering on the "sticky side" of the back piece of velcro on, to just keep the sticky covered). Now you have a gauge-on-a-wooden-stick, that you can stick into the substrate anywhere in the tank, and move whenever you want. If you are still in a 10g with only 5-6 inches of substrate, you might want to break the chopstick off a bit shorter so that when it is stood up in the substrate it is not 5 inches above the substrate, but only about 2 or 3 (it's a good idea to have them as close to the substrate as you can, while being high enough so that crabs don't easily climb on them--it just keeps them cleaner if they aren't climbed all over). The chopsticks are thin enough that they don't seem to be an invitation to climb up them (at least ours don't bother with them).

I also have some stuck onto some scrap pieces of acrylic left over from making acrylic lids for tanks. You can do the same thing with a plastic ruler you don't need anymore (again, you'll probably want to snap it off shorter than the full 12 inches, unless your substrate is already 8 inches deep or more), or with craft popsicle sticks I suppose (although they may be too short to stand well and still keep the gauge a couple of inches above the substrate). For this kind of "gauge-on-a-stick", you go ahead and take the paper off the back of the velcro and stick it right onto your piece of acrylic (or plastic ruler, or whatever). Again, you now have a gauge you can set up anywhere in the tank by sticking the support into the substrate.

By having the gauges-on-a-stick, you can easily change their locations, or easily move them into a whole new crabitat (or an iso, if/when you have to set one up). If you stick them onto the actual tank wall, then you can't move them, and they only tell you what the conditions are in that one place. Also, they limit how you can redesign the tank, because you can't add substrate any deeper than right below them, and you have to make sure any decor doesn't make it so you can't see them. Also, if you find you need a UTH on the side of the tank where you have stuck the gauges, then the gauges stuck on the wall there become useless.

As for placement of your gauges-on-a-stick, what you want to know first off is how the temp and humidity are in the places where the crabs spend the most time; so, near the substrate, generally, and near wherever they stay most of the day (if they aren't digging under during the day). If you have hanging or raised levels you can put your gauges in or on those for awhile too to see how the temp/humidity is up there as well; and it's good to know how temp and humidity vary in brightly lit vs. shadier parts of the tank.

You need to leave the gauges in one place, with the lid on, for a while (I'd say at least an hour), to make sure the reading is really reflecting the conditions. Best wishes for healthy conditions.

Oh--incidentally, I have discovered that I can use the same chopstick trick with these digital gauges from Lowe's:

http://www.lowes.com/pd_396632-53921-00309___

I just stick the narrower end of the chopstick up into the "hanging hole" on the back of these, and stand them up in the substrate. The angle turns out to be perfect for reading as you are looking down into the tank from the top. It should be said that I only have one crab up and active at this time; once more are up and digging, this may be too "top-heavy" to keep like this.

I previously had one like this attached to the back of the tank with some super-magnets; but those are incredibly expensive, and didn't hold up to a curious crab trying to climb on the gauge. So, I'm not sure what I'll do if the chopstick method won't work in the spring. I do love how easy these are to read, though!

thanks - and again please remind me of what they should read at

Humidity needs to be 75% or HIGHER. This is extremely important, since these crabs breathe with modified gills, they need sufficient humidity in the air to be able to breathe.

Temperature, for Purple Pinchers (most common type of crab sold in U.S.) should also be at least 75 degrees (F). A good rule of thumb is to shoot for "80 and 80" because that's easy to remember, but PP's are fine anywhere between 75 degrees F to up in the 90's (during the hottest part of their day; they don't need constant temps in the 90's); and humidity varying from 75% to up in the 90's is also fine. Note that as temp goes up, relative humidity will go down, and vice-versa, so it is always a balancing act to get both in the "friendly range."

bullshop wrote:oh stands in the tank?? can you link me to it so I can see it please?

This is the unit. The only issue I have with it, as do many other crabbers, is that the humidity affects the digital readout after a while. This is the second one I've had in the past year and it's already starting to get wonky.
http://www.walmart.com/ip/AcuRite-Digit ... r/16888914

This is unit I plan to get to replace the Acurite when its screen is no longer readable. This type of thermometer/hygrometer is a dual "plus": only the probe goes into the tank and said probe can easily be placed in different areas for readings tank-wide.
http://www.reptilebasics.com/thermometers/TH-100/

If you're staying with the "stick-on" type thermometer/hygrometer, @Dragonfly's suggestion re mounting it to a ruler or chopstick is excellent and one I'd never even thought of.