HCA: Hermit Crab Association

I was looking into purchasing a tall glow selenite tower for my tank (to add some "wow" factor to to the display), it would basically be buried under the substrate and the LED would be underneath the tank with my heat packs. A selenite crystal is basically a huge block of calcium sulfate found in caves. From what I'm reading, Calcium Sulfate is used in tofu, toothpaste, plaster of paris, the white rocks in fertilizer that decrease heavy metal toxicity. but I've also read that it dissolves very slowly over time with humidity. Would this item be deemed "safe" in a crabitat?

Did some research on Calcium Sulfate toxicity ie aquatic and couldn't find much relevant information because its widely considered to be non-toxic at certain levels but because hermitcrabs are so much smaller than us the reduction in body volume will cause things that are not toxic to larger animals to become toxic to the crabs very quickly and because they will eat on this wearing it down pretty rapidly you also have to be concerned with any electrical wiring becoming exposed because they will also nip into the wires and that could lead to a potential electrocution risk.

My opinion on this is not to use it in the hermitcrab enclosure.

You stated that your using bottom mounted heat sources for your enclosure its actually recommended to only back or side mount your heat pads because bottom mounting leads to an encapsulation of the heat emitted by the pad because of the depth and dampness of the substrate we use it actually tends to act like an insulating barrier trapping the heat around the area the pad is mounted and will quickly cause the temp to rise to well above one hundred degrees which will overheat and cook burrowed or molting hermitcrabs.

You have to think about heating a hermitcrab enclosure in terms of what is natural to the crabs and in nature hermitcrabs dig down to get away from the heat of the day so putting a heat source where one doesn't exist naturally is actually counter-intuitive and can lead to the accidental deaths of molting or burrowed crabs.

ok good point, I'll switch over the heat pads to the side.

Regarding the selenite, the more I think about it, I agree that it sounds like a bad idea. The selenite might alter the substrate's pH by adding more calcium into the substrate. If anything should be put in the tank it should be completely inert and aquarium grade, like quartz.

Just adding my two-cents worth as to why selenite would be a no-go for a crabitat. I'm a docent at a natural history museum and our Mineral Hall is my territory. We have three gorgeous samples of selenite in the Hall, from large ram's horn to thin glassine spikes, all in airtight cases -- this is due to selenite's tendency to disintegrate when kept in a humid atmosphere. Selenite is a cave mineral (same chemical formula as its cousin calcite) and forms in dampness; however, once it has been removed from its natural habitat, dampness becomes its enemy and it starts to erode in a most unpleasant manner: it sheds tiny splinters!

If you really want the look; maybe see if you can get a "plastic substitute" that looks like the real thing. I'm sure that there is an item out there that would work.

A while back, I was watching fish tank kings and they had to make a glowing crystal type tank.. Which turned into being bamboo... Any way, when trying out different "crystal" ideas they took some square acrylic and cut it into a crystalline shape, add an LED below it... There ya go.


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I followed your advice and looked into acrylic crystals, and they are absolutely exquisite. Some artists carve faces into the acrylic pieces. "Lucite", or acrylic crystals, are translucent and scatter the light nicely throughout the medium. When shining a light beneath the piece, it adds an ambient light to the surroundings, highlighting the bottom sides of driftwood and foliage. I ended up getting a scratched acrylic trophy for cheap because the lucite statues were too expensive. Can't wait to show the finished tank after we move in December!

After doing loads of research, Lucite is really the only option for a tank. Any other medium has some kind of a caveat: Selenite and fluorite dissolve. Some crystal glass has lead or boron and is known to leech into water (non-leaded glass has a green tint to it). Even some colored quartz are irradiated to give them a smokey or amethyst look, and sometimes remain radioactive for a few months past their color enhancement. Regardless I'm super satisfied with using lucite.