Heat/Humidity Dilemma?

[kayepaye]

So I currently have my 6 small crabs in a 10G, but moving them into a 40GB ASAP.

I was having a really hard time with humidity, it was going down to 20% even with spraying 5x a day.
I purchased a humidifier for the tank, and installed it last night after doing a full clean out, and adding more substrate.
The humidity went up to 80%, and then overnight it's gone down to 40%-50% and is holding steady there. I've sprayed it several times, but would like to avoid doing that constantly.

The heat is now up to 90 degrees, and I'm worried that it's too hot in there for them.
If I turn the heat lamp off, it drops like 20 degrees within 5 minutes.

This has been the most stressful endeavor I've ever taken on, but I'm anxiously waiting for the moment when everything calms down and I can really enjoy my new babies.

My ultratherm came in the mail yesterday, so I'm going to install that as soon as I get the chance, but what if the ultratherm makes my tank too hot? Is there anything I can do to not have it on full power?

My tank has 6" of substrate (used to do 5:1 sand/ee but now doing 3:1 sand/ee as it was drying out too fast), I am using cat food dishes as my pools, 1 for fresh water and 1 for salt (I will be installing a bigger salt water pool when I get my 40G). I have a huge shell shop, a hidey house, a food dish, and I have a moss pit but there's really no room for it, so I'm going to be suspending the shell shop and putting the moss pit on the ground.
Once I get the 40G I'll have room for everything, so that will be a nice change!

[wodesorel]

Have you calibrated your hygrometer to make sure it's reading correctly? Swings that severe can happen, especially in winter with a furnace running in the house, but that is some extreme humidity changes and it could be a sign of a broken humidity gauge. (Also, most new guages don't read correctly out of the box!) What kind of lid do you have on the 10 gallon?

If the Ultratherm does run too hot, you can buy a plug-in lamp dimmer from any hardware store for under $12. It has a slide that allows you restrict the flow of electricity to the pad which in turn makes it run cooler. You'll have to play around with it a bit to find the right setting for your tank, and if the room temperature changes you'll have to make adjustments as well.

[kayepaye]

Have you calibrated your hygrometer to make sure it's reading correctly? Swings that severe can happen, especially in winter with a furnace running in the house, but that is some extreme humidity changes and it could be a sign of a broken humidity gauge. (Also, most new guages don't read correctly out of the box!) What kind of lid do you have on the 10 gallon?

If the Ultratherm does run too hot, you can buy a plug-in lamp dimmer from any hardware store for under $12. It has a slide that allows you restrict the flow of electricity to the pad which in turn makes it run cooler. You'll have to play around with it a bit to find the right setting for your tank, and if the room temperature changes you'll have to make adjustments as well.

I have 2 hygrometers in the tank(1 on each side) both are showing the same readings, I'm assuming that they are correct, but I'll calibrate them both to be sure.