HCA: Hermit Crab Association

I have a 125 gallon tank and I'm thinking of attaching a 75 gallon tank on the top of it. I'm worried that it will be too cold so I was thinking of adding a UTH on the back of it. For people who do have toppers, what do you do?

Thanks

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I have been feeding it to them them for a while but just now realized the ingredients. I imagine that it is safe because nothing has happened to them.

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Here's a picture of it

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I bought organic spring mix at walmart and there are foods in it that are not on the safe food list. It's arugula, mizuna, tatsoi, and frisee. Are they safe?

I just use sand

This is what it looks like

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What is the black splotches in my sand? Is it their poop? I have A LOT of isopods in my tank, does it have to do with them? I took out a fake plant and this is what was under it.

I am wondering if I am setting up my tank wrong. When I see hermit crab tank setups there are always a bunch of space in the front and climbing/hide decorations in the back of the tank. My setup isn't like that so I'm wondering if it's required.

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I'll get some cuttlebone at walmart and crush some oysters shells that I have. I'll mix in some crushed oyster shells, calcium carbonate supplement, and some egg shells in a dish for them to access anytime.

I am wondering if it's alright to sprinkle calcium carbonate supplement on my crabs food everyday. I feed veggies which contains calcium and some shrimp with the exoskeleton attached. I have been sprinkling the calcium carbonate supplement on their food everyday for a while now. I don't have cuttleb...