HCA: Hermit Crab Association

I saw something white at the edge of the sub, and picked at it, thinking it was a chunk of eggshell or something. Turns out it was what appears to be salt build up. And not just a little, big hunks of it. I used fresh water to mix all my sub, and haven't really ever needed to mist. If I add water, it's always RO along the edges. Would this much salt have built up just from them spilling their water over the years?

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Could be salt creep. I think it’s a saltwater aquarium term. Basically just a build up over time. Is it near your saltwater pool?


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It's very likely not salt! At least, not the sodium chloride mix you're thinking of. There are other types of cystaline solids that are in freshwater, and they can react with the silicon dioxide in the sand and form concretions like this. It's most likely gypsum, especially if you're in the midwest. I get the same hardness around my UTHs!

Yes, it seems to be on the sides and back where my UTH's are, not on the front. I live rurally, and we have a well - but we can't drink the well water, so have to buy our drinking water. It is RO water, from the local farm supply store. That's all I have ever used in the tank, no other water. I was surprised to see this, but am glad it's not salt! And I presume I can just remove it and all is good?!

Okay, so that is a little more interesting since RO is mineral-less. Usually you'd see buildup like this from normal tap water. It's like the hard water stains you'd get on your faucet times 1000. (You should see the calcium buildup we get inside our hot water tank! We have to change our heating elements yearly or they break. Last time it was 3/4 of an inch thick.)

However, playsand does contain limestone, which is calcium based. RO water would easily dissolve limestone, and the evaporation effect around the UTH would cause it to concentrate in that area. It could certain be or contain the salt mix from the pools, but I still think it's likely from the substrate instead.

And yes, you can just pop it off and discard it when it gets bad! Anything stuck to the glass should come off easily with a razor blade or vinegar. (Once the UTH has been off for a little while so there isn't a temperature difference in the glass.)