Tufa in shrimp tank?

[Forestshrimp]

I got some rocks a long time ago from a geothermal spring. They might be some kind of grey tufa. Are these safe for shrimp?

[sliphorn]

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I am going to say yes based on the fact that I have used all kinds of rocks that I have gotten from rivers, lakes, streams and dug up in my back yard. One of my most beautiful and productive tanks is loaded with quartz I dug up in Arkansas and sandstone from my property.
I am always sure to add a bit of aragonite for buffering which I see you have done too. In fact the grey rock you have might be mostly calcium seeing as it came from a geothermal area.
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[Forestshrimp]

From what I know tufa is basically limestone, so the water is just going to be a little harder I guess