agricultural lime vs. food grade calcium carbonate

biochemnerd808

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Most of my tortoises help themselves to cuttlefish bone, which I buy in bulk and offer freely throughout the tortoise garden. However, 2 of my females don't ever partake, and those 2 females happen to be nesting now. I've observed one of them eating soil, which leads me to think that she is seeking out calcium sources. I have tried all the usual 'getting-the-tortoise-to-eat-cuttlefish' tricks, and they do all get a healthy diet of widely varied weeds and greens and flowers. However, one of the females specifically has a history that leads me to believe that she MUST have more calcium. She will NOT touch weeds sprinkled with anything.

I am hoping to make some calcium blocks myself in the hopes that these might entice her. I have read through several threads such as THIS one and THIS one and several other threads on here, but couldn't find a clear answer as to whether I must use food grade CaCO3 (calcium carbonate), or is the agricultural lime safe to make calcium blocks out of? Cost is not an issue, I just happen to have a 50lb bag of agricultural lime flour handy that is going into my garden soil, the tortoise garden soil, and our lawn next week. Chemically the two are identical (CaCo3)- I'd imagine that the food grade stuff has fewer impurities. Thoughts?

@yagyujubei - your name came up in several of those threads. I would love your input.
 

Yvonne G

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I was also curious about using gypsum. The ingredients on the bag say it is only different kinds of calcium.
 

biochemnerd808

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I was also curious about using gypsum. The ingredients on the bag say it is only different kinds of calcium.

My concern with using gypsum would be if the sulfur contained in it would cause problems. The chemical formula is CaSO4 2H2O - which is awfully close to sulfuric acid (H2SO4). I would need to dig waaaaay back into my very dusty chemistry knowledge to figure out whether it was safe. For now I'll stick with Calcium Carbonate. :)
 

mikeh

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The Zoomed calcium block is made of CaSO4 (Calcium Sulfate). My tortoises are quite obsessed with it consuming rather large quantities. Should it be avoided?
(The block also changes color under certain moist conditions to greenish blue, would this be due to Cobalt Chloride??)
 
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