Hello.
There are several areas of concern in your crabitat so I am going to go through the questions one by one and address them.
1. Substrate needs to be 3X deeper than your largest crab, shell and all. Ideally you'd want it between 6"-12" depending on how large your crabs are. We recommend a 5:1 mix of playsand and EE. I see you are picking up playsand, so that's great!
2. Are your gauges digital or analog? Analog gauges need to be calibrated and can also be "shocked" if dropped or mishandled during shipping/stocking. (I used to cook professionally, and every time we dropped one of our thermometers, we'd have to recalibrate it!)
PP's need to be between 80°F-90°F. The average year round temperature in their natural habitat is 85 or so, and that is where you will see the most activity. Humidity no less than 75% or they risk gill damage.
75°F is the absolute lowest safe temperature your crabs can be at.
3. What sort of light are you using at night? Hermit crabs are nocturnal and need a normal day/night cycle so make sure you are using a night time bulb and not a regular day/white lightbulb.
5. Distilled water is ok in a pinch, however it lacks some elements that the crabs need and would get from dechlorinated tap water. Both the fresh and saltwater need to be dechlorinated with a product like SeaChem Prime, to remove heavy metals, chlorine/ammonia from the tap water. They need marine grade salt mix. Most of us use Instant Ocean. The Zoo Med salt mix won't hurt them but isn't helping them any either.
5. Hermit crabs are scavengers and need a varied diet. Protein and calcium sources are important. Please check out our Safe Food List linked in the care guide I am linking below.
http://www.hermitcrabassociation.com/ph ... hp?t=92457
Calcium/chitin sources are essential for exoskeleton health. Cuttlebone, eggshells, dried shrimp, insects, and smashed seashells are all good sources.
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